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

Leveraging the Immunological Impacts of Irreversible Electroporation as a New Frontier for Cancer Therapy

Irreversible electroporation (IRE) is a nonthermally mediated tissue ablation modality that makes use of short pulsed electric fields to destroy cancerous lesions in situ. In the past two decades, IRE has established itself not only as an effective means to ablate small, unresectable tumor masses but also as a tool particularly qualified to modulate the tumor microenvironment in a way that dismantles pathways of cancer immunosuppression and permits the development of a systemic antitumor immune response. However, despite its immune-stimulating tendencies, for most cancers conventional IRE alone is insufficient to establish an immune response robust enough to fully eliminate disseminated disease and prevent recurrence. Here, we describe the current understanding of the histological and immunological effects of IRE, as well as recent efforts to optimize IRE parameters and develop rational combination therapies to increase the efficacy of the resulting immune response.

Effects of Interphase and Interpulse Delays on Tissue Impedance and Pulsed Field Ablation

PURPOSE

High-frequency irreversible electroporation (H-FIRE) is a pulsed field ablation (PFA) technique that employs a series of high-voltage, microseconds-long positive and negative pulses, separated by interphase (d1) and interpulse (d2) delays to non-thermally ablate tissue. Previous experimental and computational data suggest an impact of delays on nerve excitation and electrochemical effects. However, the impact of delays on PFA outcomes, such as change in resistance and ablation generation, has only recently started to be elucidated.

METHODS

While recording the applied voltage and currents, we delivered a series of increasing voltages, termed voltage ramps, into tuber and cardiac tissues using both needle electrode pairs and flat plate electrodes. Tissues were stained for metabolic activity to measure irreversible electroporation areas following treatment.

RESULTS

Our findings support previous in vitro data that delays do not significantly affect ablation areas. While there were significant differences in applied current, resistance, and conductivity between different pulse widths at sub-electroporation electric fields, we found no significant differences after inducing electroporation between different delays and pulse widths. Consequently, since delays do not affect ablation areas or local conductivity, the data suggests that delays should not affect the electric field threshold or Joule heating within the tissue.

CONCLUSION

The findings presented here provide critical insights into electroporation-dependent tissue conductivity changes from H-FIRE with implications for improving H-FIRE parameterization and computational models for treatment planning in cancer and cardiac pulsed field ablation.

Caspase-Dependent Cell Death and HDAC4 Translocation Following Microsecond Pulsed Electric Field (μsPEF) Exposure in MCF-7 Breast Cancer Cells

Breast cancer is the second-leading cancer-related death among women. Survival rates decrease from 99% for localized stages of breast tumors to only 27% when distant metastases develop. Increased invasiveness and proliferation of breast cancer cells correlate with overexpression of an enzymatic coregulator of gene expression, histone deacetylase-4 (HDAC4). If HDAC4 is cleaved into two halves by another enzyme called caspase, one-half of HDAC4 goes into the nucleus of the cell where it promotes a highly regulated form of cellular self-destruction known as apoptosis. Caspases are activated by fast rises in calcium ion (Ca2+) concentrations inside cells, which can be initiated via plasma membrane electropermeabilization induced by microsecond pulsed electric fields (µsPEFs) applied to cells positioned between electrodes. However, the MCF-7 breast cancer cell line is deficient in caspase-3, which is the type of caspase predominantly responsible for cleavage of HDAC4. In this in vitro study, we demonstrate µsPEF exposure elicits HDAC4 translocation independently of caspase activity in MCF-7 cells. Yet, µsPEF-induced MCF-7 cell death remains dependent on Ca2+ electropermeabilization and caspase activity. Bioelectromagnetics. 00:00-00, 2025. © 2025 © 2025 Bioelectromagnetics Society.

Pulsed field ablation in medicine: irreversible electroporation and electropermeabilization theory and applications

BACKGROUND

Focal ablation techniques are integral in the surgical intervention of diseased tissue, where it is necessary to minimize damage to the surrounding parenchyma and critical structures. Irreversible electroporation (IRE) and high-frequency IRE (H-FIRE), colloquially called pulsed-field ablation (PFA), utilize high-amplitude, low-energy pulsed electric fields (PEFs) to nonthermally ablate soft tissue. PEFs induce cell death through permeabilization of the cellular membrane, leading to loss of homeostasis. The unique nonthermal nature of PFA allows for selective cell death while minimally affecting surrounding proteinaceous structures, permitting treatment near sensitive anatomy where thermal ablation or surgical resection is contraindicated. Further, PFA is being used to treat tissue when tumor margins are not expected after surgical resection, termed margin accentuation. This review explores both the theoretical foundations of PFA, detailing how PEFs induce cell membrane destabilization and selective tissue ablation, the outcomes following treatment, and its clinical implications across oncology and cardiology.

CONCLUSIONS

Clinical experience is still progressing, but reports have demonstrated that PFA reduces complications often seen with thermal ablation techniques. Mounting oncology data also support that PFA produces a robust immune response that may prevent local recurrences and attenuate metastatic disease. Despite promising outcomes, challenges such as optimizing field delivery and addressing variations in tissue response require further investigation. Future directions include refining PFA protocols and expanding its application to other therapeutic areas like benign tissue hyperplasia and chronic bronchitis.

Toward Large Ablations With Single-Needle High-Frequency Irreversible Electroporation In Vivo

Irreversible electroporation (IRE) is a minimally thermal tissue ablation modality used to treat solid tumors adjacent to critical structures. Widespread clinical adoption of IRE has been limited due to complicated anesthetic management requirements and technical demands associated with placing multiple needle electrodes in anatomically challenging environments. High-frequency irreversible electroporation (H-FIRE) delivered using a novel single-insertion bipolar probe system could potentially overcome these limitations, but ablation volumes have remained small using this approach. While H-FIRE is minimally thermal in mode of action, high voltages or multiple pulse trains can lead to unwanted Joule heating. In this work, we improve the H-FIRE waveform design to increase the safe operating voltage using a single-insertion bipolar probe before electrical arcing occurs. By uniformly increasing interphase () and interpulse () delays, we achieved higher maximum operating voltages for all pulse lengths. Additionally, increasing pulse length led to higher operating voltages up to a certain delay length (25 μs), after which shorter pulses enabled higher voltages. We then delivered novel H-FIRE waveforms via an actively cooled single-insertion bipolar probe in swine liver in vivo to determine the upper limits to ablation volume possible using a single-needle H-FIRE device. Ablations up to 4.62 0.12 cm x 1.83 0.05 cm were generated in 5 minutes without a requirement for cardiac synchronization during treatment. Ablations were minimally thermal, easily visualized with ultrasound, and stimulated an immune response 24 hours post H-FIRE delivery. These data suggest H-FIRE can rapidly produce clinically relevant, minimally thermal ablations with a more user-friendly electrode design.

Maps of Membrane Pore Dynamics From Picosecond to Millisecond Pulse Durations

Electroporation occurs when cells are exposed to an electric pulse of sufficient intensity and pulse duration . Many studies have attempted to develop universal scaling laws to predict membrane pore dynamics for pulsed electric fields (PEFs) of different durations; however, the differences in pore dynamics across these parameters makes this difficult both experimentally and numerically. This study uses the asymptotic Smoluchowski equation (ASME) to quantify the number of pores, average pore radius, and fractional pore area (FPA) during exposure to PEFs with durations from hundreds of picoseconds to a millisecond. We highlight pulse parameter regimes that favor increases in pore radius and number and show that the FPA is dominated by the number of pores formed on the cell membrane. Furthermore, the number of pores and the FPA depend almost entirely on for exceeding the charging time of the cell and both and for shorter than the charging time. Finally, the maps of pore number, average radius, and FPA demonstrate that a universal scaling law for pore dynamics across a wide range of pulse durations does not exist, although certain scaling behaviors may be valuable over narrow regimes. Practically, these maps provide a guideline for selecting PEF parameters to achieve desired membrane permeabilization.

Biophysics and electrophysiology of pulsed field ablation in normal and infarcted porcine cardiac ventricular tissue

Pulsed Field Ablation (PFA) is a new ablation method being rapidly adopted for treatment of atrial fibrillation, which shows advantages in safety and efficiency over radiofrequency and cryo-ablation. In this study, we used an in vivo swine model (10 healthy and 5 with chronic myocardial infarct) for ventricular PFA, collecting intracardiac electrograms, electro-anatomical maps, native T1-weighted and late gadolinium enhancement MRI, gross pathology, and histology. We used 1000-1500 V pulses, with 1-16 pulse trains to vary PFA dose. Lesions were assessed at 24 h, 7 days, and 6 weeks in healthy and at 48 h in infarcted ventricles. Comparisons of lesion sizes using a numerical model enabled us to determine lethal electric field thresholds for cardiac tissue and its dependence on the number of pulse trains. Similar thresholds were found in normal and infarcted hearts. Numerical modeling and temperature-sensitive MRI confirmed the nonthermal nature of PFA, with less than 2% of a lesion's volume at the highest dose used being attributed to thermal damage. Longitudinal cardiac MRI and histology provide a comprehensive description of lesion maturation. Lesions shrink between 24 h and 7 days post-ablation and then remain stable out to 6 weeks post-ablation. Periprocedural electrograms analysis yields good correlation with lesion durability and size.

Modulating the Cell Death Immune Response for Electroporation Treatments

Irreversible electroporation (IRE) is a minimally invasive ablation technique that compromises integrity of the cell membrane through the application of short duration, high voltage electric pulses to induce cell death. Adverse effects of IRE such as muscle contractions are reduced with higher frequency biphasic pulsing, commonly known as high-frequency irreversible electroporation (H-FIRE). IRE and H-FIRE treatments have shown to increase immune activation through the induction of both immediate and delayed cell death, indicated by the release of damage-associated molecular pathways, antigens, and proteins. In this study, we demonstrated that specific modes of cell death can be elicited by modifying the applied pulse width and electric field strength of various waveforms. Several assays were performed on a human glioblastoma cell line, seeded onto a 2D monolayer for electroporation treatments. Cleavage of Caspase 3/7 and Caspase 1, well-known indicators of apoptosis and pyroptosis, respectively, was quantified. Our results indicate that apoptotic activity was increased for shorter pulse widths and stronger electric fields, whereas pyroptotic activity displayed opposite trends being significantly dominant with longer pulse widths at lower applied electric fields. When clinically applied, the activation of specific cell death mechanisms can allow for controlling the extent of an electroporation-mediated immune response and subsequently improved overall patient survival. With this information, we could use an electrode array to spatially manipulate the elicited immune response for patient-specific treatments.

Advances in irreversible electroporation for prostate cancer

Irreversible electroporation is a nonthermal ablation technique that uses a high-voltage electric current to create nanosized pores in the cell membrane of a malignant tumor, thus resulting in cell death. In recent years, an increasing number of clinical studies have shown that irreversible electroporation is a safe and effective treatment for prostate cancer. We describe the progress of irreversible electroporation in prostate cancer in recent years in terms of its mechanism of action, clinical studies, advantages and disadvantages and summarize the gaps in existing studies and directions for future research.

Irreversible Electroporation Margin Accentuation in Pancreaticoduodenectomy: A Propensity Score Matching Analysis

BACKGROUND

Margin accentuation using irreversible electroporation (MA-IRE) improves recurrence and overall survival (OS) in pancreatic cancer patients; however, there have been limited outcome comparisons to similarly risked patients who did not receive MA-IRE.

METHODS

Patients with borderline resectable or locally advanced pancreatic adenocarcinoma who underwent a pancreaticoduodenectomy (PD) between 2017 and 2022 were included. Those who did not receive neoadjuvant chemotherapy for major vessel involvement were excluded. One-to-one propensity score matching (PSM) was used to match the MA-IRE group with the corresponding non-MA-IRE control group with similar risk factors.

RESULTS

A total of 36 patients were included in this study. Seventeen (47.2%) patients who underwent MA-IRE matched with 19 control patients (52.8%) with similar risk factors who did not have MA-IRE. Before matching, OS and disease-free survival (DFS) were comparable between the MA-IRE and non-MA-IRE groups. After matching, the MA-IRE group showed improved OS (746 vs. 509 days, hazard ratio 0.313; p = 0.034) compared with the non-MA-IRE group. DFS (p = 0.768), negative margin status (p = 0.317), and 30-day complication rates (p = 1.000) remained statistically different between the groups.

CONCLUSIONS

MA-IRE in PD results in longer OS but does not impact margin status, DFS, or postoperative complication rates in our cohort. These findings suggest that MA-IRE is safe and potentially promotes immune cell activation rather than upfront margin mitigation.

Investigation of High Frequency Irreversible Electroporation for Canine Spontaneous Primary Lung Tumor Ablation

In this study, the feasibility of treating canine primary lung tumors with high-frequency irreversible electroporation (H-FIRE) was investigated as a novel lung cancer treatment option. H-FIRE is a minimally invasive tissue ablation modality that delivers bipolar pulsed electric fields to targeted cells, generating nanopores in cell membranes and rendering targeted cells nonviable. In the current study, canine patients (n = 5) with primary lung tumors underwent H-FIRE treatment with an applied voltage of 2250 V using a 2-5-2 µs H-FIRE waveform to achieve partial tumor ablation prior to the surgical resection of the primary tumor. Surgically resected tumor samples were evaluated histologically for tumor ablation, and with immunohistochemical (IHC) staining to identify cell death (activated caspase-3) and macrophages (IBA-1, CD206, and iNOS). Changes in immunity and inflammatory gene signatures were also evaluated in tumor samples. H-FIRE ablation was evident by the microscopic observation of discrete foci of acute hemorrhage and necrosis, and in a subset of tumors (n = 2), we observed a greater intensity of cleaved caspase-3 staining in tumor cells within treated tumor regions compared to adjacent untreated tumor tissue. At the study evaluation timepoint of 2 h post H-FIRE, we observed differential gene expression changes in the genes IDO1, IL6, TNF, CD209, and FOXP3 in treated tumor regions relative to paired untreated tumor regions. Additionally, we preliminarily evaluated the technical feasibility of delivering H-FIRE percutaneously under CT guidance to canine lung tumor patients (n = 2). Overall, H-FIRE treatment was well tolerated with no adverse clinical events, and our results suggest H-FIRE potentially altered the tumor immune microenvironment.

Integrating electromagnetic cancer stress with immunotherapy: a therapeutic paradigm

An array of published cell-based and small animal studies have demonstrated a variety of exposures of cancer cells or experimental carcinomas to electromagnetic (EM) wave platforms that are non-ionizing and non-thermal. Overall effects appear to be inhibitory, inducing cancer cell stress or death as well as inhibition in tumor growth in experimental models. A variety of physical input variables, including discrete frequencies, amplitudes, and exposure times, have been tested, but drawing methodologic rationale and mechanistic conclusions across studies is challenging. Nevertheless, outputs such as tumor cytotoxicity, apoptosis, tumor membrane electroporation and leak, and reactive oxygen species generation are intriguing. Early EM platforms in humans employ pulsed electric fields applied either externally or using interventional tumor contact to induce tumor cell electroporation with stromal, vascular, and immunologic sparing. It is also possible that direct or external exposures to non-thermal EM waves or pulsed magnetic fields may generate electromotive forces to engage with unique tumor cell properties, including tumor glycocalyx to induce carcinoma membrane disruption and stress, providing novel avenues to augment tumor antigen release, cross-presentation by tumor-resident immune cells, and anti-tumor immunity. Integration with existing checkpoint inhibitor strategies to boost immunotherapeutic effects in carcinomas may also emerge as a broadly effective strategy, but little has been considered or tested in this area. Unlike the use of chemo/radiation and/or targeted therapies in cancer, EM platforms may allow for the survival of tumor-associated immunologic cells, including naïve and sensitized anti-tumor T cells. Moreover, EM-induced cancer cell stress and apoptosis may potentiate endogenous tumor antigen-specific anti-tumor immunity. Clinical studies examining a few of these combined EM-platform approaches are in their infancy, and a greater thrust in research (including basic, clinical, and translational work) in understanding how EM platforms may integrate with immunotherapy will be critical in driving advances in cancer outcomes under this promising combination.

Synergistically Augmenting Cancer Immunotherapy by Physical Manipulation of Pyroptosis Induction

Pyroptosis is a newly recognized type of programmed cell death mediated by the gasdermin family and caspase. It is characterized by the formation of inflammasomes and the following inflammatory responses. Recent studies have elucidated the value of pyroptosis induction in cancer treatment. The inflammatory cytokines produced during pyroptosis can trigger immune responses to suppress malignancy. Physical approaches for cancer treatment, including radiotherapy, light-based techniques (photodynamic and photothermal therapy), ultrasound-based techniques (sonodynamic therapy and focused ultrasound), and electricity-based techniques (irreversible electroporation and radiofrequency ablation), are effective in clinical application. Recent studies have reported that pyroptosis is involved in the treatment process of physical approaches. Manipulating pyroptosis using physical approaches can be utilized in combating cancer, according to recent studies. Pyroptosis-triggered immunotherapy can be combined with the original anti-tumor methods to achieve a synergistic therapy and improve the therapeutic effect. Studies have also revealed that enhancing pyroptosis may increase the sensitivity of cancer cells to some physical approaches. Herein, we present a comprehensive review of the literature focusing on the associations between pyroptosis and various physical approaches for cancer and its underlying mechanisms. We also discussed the role of pyroptosis-triggered immunotherapy in the treatment process of physical manipulation.

Irreversible electroporation promotes a pro-inflammatory tumor microenvironment and anti-tumor immunity in a mouse pancreatic cancer model

Pancreatic cancer is a significant cause of cancer-related mortality and often presents with limited treatment options. Pancreatic tumors are also notorious for their immunosuppressive microenvironment. Irreversible electroporation (IRE) is a non-thermal tumor ablation modality that employs high-voltage microsecond pulses to transiently permeabilize cell membranes, ultimately inducing cell death. However, the understanding of IRE's impact beyond the initiation of focal cell death in tumor tissue remains limited. In this study, we demonstrate that IRE triggers a unique mix of cell death pathways and orchestrates a shift in the local tumor microenvironment driven, in part, by reducing the myeloid-derived suppressor cell (MDSC) and regulatory T cell populations and increasing cytotoxic T lymphocytes and neutrophils. We further show that IRE drives induce cell cycle arrest at the G0/G1 phase in vitro and promote inflammatory cell death pathways consistent with pyroptosis and programmed necrosis in vivo. IRE-treated mice exhibited a substantial extension in progression-free survival. However, within a span of 14 days, the tumor immune cell populations reverted to their pre-treatment composition, which resulted in an attenuation of the systemic immune response targeting contralateral tumors and ultimately resulting in tumor regrowth. Mechanistically, we show that IRE augments IFN- γ signaling, resulting in the up-regulation of the PD-L1 checkpoint in pancreatic cancer cells. Together, these findings shed light on potential mechanisms of tumor regrowth following IRE treatment and offer insights into co-therapeutic targets to improve treatment strategies.

A novel method for septal reduction therapy by three-dimensional guided transvenous intraseptal pulsed-field ablation

BACKGROUND

Pulsed-field ablation (PFA) is a nonthermal method for achieving selective cell death with little inflammation response. However, there are no reports of PFA for septal reduction therapy (SRT).

OBJECTIVE

The purpose of this study was to investigate the effectiveness and safety of PFA for SRT.

METHODS

A novel transvenous intraseptal PFA method with 3-dimensional (3D) guidance was introduced in Yorkshire pigs. Electrocardiographic parameters, transthoracic echocardiography, and histopathology were used to evaluated.

RESULTS

The maximum injury diameter of intramyocardial PFA increased with electric field intensity. After PFA, bipolar electrogram amplitude and pacing threshold measured by the PFA electrodes significantly decreased (F = 6.945, P = .007) or increased (F = 5.842, P = .024), respectively. In the ablated septal region, motion amplitude and systolic wall thickening rate significantly decreased and remained at low levels (motion amplitude: F = 20.793, P = .000; systolic wall thickening rate: F = 14.343, P = .000); however, septal thickness did not significantly change after PFA (F = 1.503, P = .248). Histologic examination showed specific cardiomyocyte death with gradually increased hyperchromatic cytoplasm and nuclear pyknosis, without obvious inflammatory cell infiltration in acute phase. TUNEL stain for fragmented DNA showed extensively positive in the ablation region 24 hours after PFA. During PFA, no sustained ventricular arrhythmia or atrioventricular conduction block occurred.

CONCLUSION

A novel intraseptal PFA method with 3D guidance was described. Intraseptal PFA resulted in effective myocardial injury and local hypokinesis without significant acute edema. Histologic examination showed widely programmed cardiomyocyte death with little inflammatory cell infiltration.

Characterizing reversible, irreversible, and calcium electroporation to generate a burst-dependent dynamic conductivity curve

The relationships between burst number, reversible, irreversible, and calcium electroporation have not been comprehensively evaluated in tumor tissue-mimics. Our findings indicate that electroporation effects saturate with a rate constant (τ) of 20 bursts for both conventional and high frequency waveforms (R2 > 0.88), with the separation between reversible and irreversible electroporation thresholds converging at 50 bursts. We find the lethal thresholds for calcium electroporation are statistically similar to reversible electroporation (R2 > 0.99). We then develop a burst-dependent dynamic conductivity curve that now incorporates electroporation effects due to both the electric field magnitude and burst number. Simulated ablation and thermal damage volumes vary significantly between finite element models using either the conventional or new burst-dependent dynamic conductivity curve (p < 0.05). Lastly, for clinically relevant protocols, thermal damage is indicated to not begin until 50 bursts, with maximum nonthermal ablation volumes at 100 bursts (1.5-13% thermal damage by volume). We find that >100 bursts generated negligible increases in ablation volumes with 40-70% thermal damage by volume at 300 bursts. Our results illustrate the need for considering burst number in minimizing thermal damage, choosing adjuvant therapies, and in modeling electroporation effects at low burst numbers.

Dynamics of Cell Death Due to Electroporation Using Different Pulse Parameters as Revealed by Different Viability Assays

The mechanisms of cell death due to electroporation are still not well understood. Recent studies suggest that cell death due to electroporation is not an immediate all-or-nothing response but rather a dynamic process that occurs over a prolonged period of time. To investigate whether the dynamics of cell death depends on the pulse parameters or cell lines, we exposed different cell lines to different pulses [monopolar millisecond, microsecond, nanosecond, and high-frequency bipolar (HFIRE)] and then assessed viability at different times using different viability assays. The dynamics of cell death was observed by changes in metabolic activity and membrane integrity. In addition, regardless of pulse or cell line, the dynamics of cell death was observed only at high electroporation intensities, i.e., high pulse amplitudes and/or pulse number. Considering the dynamics of cell death, the clonogenic assay should remain the preferred viability assay for assessing viability after electroporation.

Engineering high post-electroporation viabilities and transfection efficiencies for elongated cells on suspended nanofiber networks

The impact of cell shape on cell membrane permeabilization by pulsed electric fields is not fully understood. For certain applications, cell survival and recovery post-treatment is either desirable, as in gene transfection, electrofusion, and electrochemotherapy, or is undesirable, as in tumor and cardiac ablations. Understanding of how morphology affects cell viability post-electroporation may lead to improved electroporation methods. In this study, we use precisely aligned nanofiber networks within a microfluidic device to reproducibly generate elongated cells with controlled orientations to an applied electric field. We show that cell viability is significantly dependent on cell orientation, elongation, and spread. Further, these trends are dependent on the external buffer conductivity. Additionally, we see that cell survival for elongated cells is still supported by the standard pore model of electroporation. Lastly, we see that manipulating the cell orientation and shape can be leveraged for increased transfection efficiencies when compared to spherical cells. An improved understanding of cell shape and pulsation buffer conductivity may lead to improved methods for enhancing cell viability post-electroporation by engineering the cell morphology, cytoskeleton, and electroporation buffer conditions.

Determination of lethal electric field threshold for pulsed field ablation in ex vivo perfused porcine and human hearts

Introduction

Pulsed field ablation is an emerging modality for catheter-based cardiac ablation. The main mechanism of action is irreversible electroporation (IRE), a threshold-based phenomenon in which cells die after exposure to intense pulsed electric fields. Lethal electric field threshold for IRE is a tissue property that determines treatment feasibility and enables the development of new devices and therapeutic applications, but it is greatly dependent on the number of pulses and their duration.

Methods

In the study, lesions were generated by applying IRE in porcine and human left ventricles using a pair of parallel needle electrodes at different voltages (500-1500 V) and two different pulse waveforms: a proprietary biphasic waveform (Medtronic) and monophasic 48 × 100 μs pulses. The lethal electric field threshold, anisotropy ratio, and conductivity increase by electroporation were determined by numerical modeling, comparing the model outputs with segmented lesion images.

Results

The median threshold was 535 V/cm in porcine ((N = 51 lesions in n = 6 hearts) and 416 V/cm in the human donor hearts ((N = 21 lesions in n = 3 hearts) for the biphasic waveform. The median threshold value was 368 V/cm in porcine hearts ((N = 35 lesions in n = 9 hearts) cm for 48 × 100 μs pulses.

Discussion

The values obtained are compared with an extensive literature review of published lethal electric field thresholds in other tissues and were found to be lower than most other tissues, except for skeletal muscle. These findings, albeit preliminary, from a limited number of hearts suggest that treatments in humans with parameters optimized in pigs should result in equal or greater lesions.

Quantitative analysis of contribution of mild and moderate hyperthermia to thermal ablation and sensitization of irreversible electroporation of pancreatic cancer cells

INTRODUCTION

Irreversible electroporation (IRE) is an ablation modality that applies short, high-voltage electric pulses to unresectable cancers. Although considered a non-thermal technique, temperatures do increase during IRE. This temperature rise sensitizes tumor cells for electroporation as well as inducing partial direct thermal ablation.

AIM

To evaluate the extent to which mild and moderate hyperthermia enhance electroporation effects, and to establish and validate in a pilot study cell viability models (CVM) as function of both electroporation parameters and temperature in a relevant pancreatic cancer cell line.

METHODS

Several IRE-protocols were applied at different well-controlled temperature levels (37 °C ≤ T ≤ 46 °C) to evaluate temperature dependent cell viability at enhanced temperatures in comparison to cell viability at T = 37 °C. A realistic sigmoid CVM function was used based on thermal damage probability with Arrhenius Equation and cumulative equivalent minutes at 43 °C (CEM43°C) as arguments, and fitted to the experimental data using "Non-linear-least-squares"-analysis.

RESULTS

Mild (40 °C) and moderate (46 °C) hyperthermic temperatures boosted cell ablation with up to 30% and 95%, respectively, mainly around the IRE threshold E_th,50% electric-field strength that results in 50% cell viability. The CVM was successfully fitted to the experimental data.

CONCLUSION

Both mild- and moderate hyperthermia significantly boost the electroporation effect at electric-field strengths neighboring E_th,50%. Inclusion of temperature in the newly developed CVM correctly predicted both temperature-dependent cell viability and thermal ablation for pancreatic cancer cells exposed to a relevant range of electric-field strengths/pulse parameters and mild moderate hyperthermic temperatures.

Recent Advancements in Electroporation Technologies: From Bench to Clinic

Over the past decade, the increased adoption of electroporation-based technologies has led to an expansion of clinical research initiatives. Electroporation has been utilized in molecular biology for mammalian and bacterial transfection; for food sanitation; and in therapeutic settings to increase drug uptake, for gene therapy, and to eliminate cancerous tissues. We begin this article by discussing the biophysics required for understanding the concepts behind the cell permeation phenomenon that is electroporation. We then review nano- and microscale single-cell electroporation technologies before scaling up to emerging in vivo applications.

PIRET-A Platform for Treatment Planning in Electroporation-Based Therapies

Tissue electroporation is the basis of several therapies. Electroporation is performed by briefly exposing tissues to high electric fields. It is generally accepted that electroporation is effective where an electric field magnitude threshold is overreached. However, it is difficult to preoperatively estimate the field distribution because it is highly dependent on anatomy and treatment parameters.

OBJECTIVE

We developed PIRET, a platform to predict the treatment volume in electroporation-based therapies.

METHODS

The platform seamlessly integrates tools to build patient-specific models where the electric field is simulated to predict the treatment volume. Patient anatomy is segmented from medical images and 3D reconstruction aids in placing the electrodes and setting up treatment parameters.

RESULTS

Four canine patients that had been treated with high-frequency irreversible electroporation were retrospectively planned with PIRET and with a workflow commonly used in previous studies, which uses different general-purpose segmentation (3D Slicer) and modeling software (3Matic and COMSOL Multiphysics). PIRET outperformed the other workflow by 65 minutes (× 1.7 faster), thanks to the improved user experience during treatment setup and model building. Both approaches computed similarly accurate electric field distributions, with average Dice scores higher than 0.93.

CONCLUSION

A platform which integrates all the required tools for electroporation treatment planning is presented. Treatment plan can be performed rapidly with minimal user interaction in a stand-alone platform.

SIGNIFICANCE

This platform is, to the best of our knowledge, the most complete software for treatment planning of irreversible electroporation. It can potentially be used for other electroporation applications.

Acute ATP loss during irreversible electroporation mediates caspase independent cell death

Irreversible electroporation (IRE) has been reported to variably cause apoptosis, necrosis, oncosis or pyroptosis. Intracellular ATP is a key substrate for apoptosis which is rapidly depleted during IRE, we sought to understand whether intracellular ATP levels is a determinant of the mode of cell death following IRE. A mouse bladder cancer cell line (MB49) was treated with electric fields while increasing the number of pulses at a fixed electric field strength, and pulse width. Cell proliferation and viability and ATP levels were measured at different timepoints post-treatment. Cell death was quantified with Annexin-V/Propidium Iodide staining. Caspase activity was measure with a fluorometric kit and western blotting. A pan-caspase (Z-VAD-FMK) inhibitor was used to assess the impact of signal inhibition. We found cell death following IRE was insensitive to caspase inhibition and was correlated with ATP loss. These findings were confirmed by cell death assays and measurement of changes in caspase expression on immunoblotting. This effect could not be rescued by ATP supplementation. Rapid and acute ATP loss during IRE interferes with caspase signaling, promoting necrosis. Cell necrosis from IRE is expected to be immunostimulatory and may be effective in cancer cells that carry mutated or defective apoptosis genes.

Irreversible Electroporation in Pancreatic Cancer-An Evolving Experimental and Clinical Method

Pancreatic cancer has no symptoms until the disease has advanced and is aggressive cancer with early metastasis. Up to now, the only curative treatment is surgical resection, which is possible in the early stages of the disease. Irreversible electroporation treatment offers new hope for patients with unresectable tumors. Irreversible electroporation (IRE) is a type of ablation therapy that has been explored as a potential treatment for pancreatic cancer. Ablation therapies involve the use of energy to destroy or damage cancer cells. IRE involves using high-voltage, low-energy electrical pulses to create resealing in the cell membrane, causing the cell to die. This review summarizes experiential and clinical findings in terms of the IRE applications. As was described, IRE can be a non-pharmacological approach (electroporation) or combined with anticancer drugs or standard treatment methods. The efficacy of irreversible electroporation (IRE) in eliminating pancreatic cancer cells has been demonstrated through both in vitro and in vivo studies, and it has been shown to induce an immune response. Nevertheless, further investigation is required to assess its effectiveness in human subjects and to comprehensively understand IRE's potential as a treatment option for pancreatic cancer.

Plant-based model for the visual evaluation of electroporated area after irreversible electroporation and its comparison to in-vivo animal data

Electroporation (EP) is widely used in medicine, such as cancer treatment, in form of electrochemotherapy or irreversible electroporation (IRE). For EP device testing, living cells or tissue inside a living organism (including animals) are needed. Plant-based models seem to be a promising alternative to substitute animal models in research. The aim of this study is to find a suitable plant-based model for visual evaluation of IRE, and to compare the geometry of electroporated areas with in-vivo animal data.For this purpose, a variety of fruit and vegetables were selected and visually evaluated after 0/1/2/4/6/8/12/16/24 h post-EP. Apple and potato were found to be suitable models as they enabled a visual evaluation of the electroporated area. For these models, the size of the electroporated area was determined after 0/1/2/4/6/8/12/16/24 h. For apples, a well-defined electroporated area was visual within two hours, while in potatoes it reached a plateau after eight hours only. The electroporated area of apple, which showed the fastest visual results was then compared to a retrospectively evaluated swine liver IRE dataset which had been obtained for similar conditions. The electroporated area of the apple and swine liver both showed a spherical geometry of comparable size. For all experiments, the standard protocol for human liver IRE was followed. To conclude, potato and apple were found to be suitable plant-based models for the visual evaluation of electroporated area after irreversible EP, with apple being the best choice for fast visual results. Given the comparable range, the size of the electroporated area of the apple may be promising as a quantitative predictor in animal tissue. Even if plant-based models cannot completely replace animal experiments, they can be used in the early stages of EP device development and testing, decreasing animal experiments to the necessary minimum.

Effects of different applied voltages of irreversible electroporation on prostate cancer in a mouse model

As a non-thermal ablation method, irreversible electroporation (IRE) has been widely investigated in the treatment of prostate cancer. However, no consensus has been achieved on the optimal parameters of IRE for prostate cancer. Since high voltage is known to carry risks of muscle contraction and patient discomfort, it is crucial to identify the minimum but effective and safer applied voltage to inhibit tumor growth. In this study, the effect of different applied voltages of IRE on prostate cancer was evaluated in BALB/c nude mice. Mathematical simulation and measurement of the actual ablation area revealed a larger ablation area at a higher voltage. In in vivo experiment, except for the three different voltages applied, all groups received identical electrical conditions: pulse number, 180 (20 groups × 9 pulses/group); pulse width, 100 µs; pulse interval, 2 ms; distance between the electrodes, 5 mm; and electrode exposure length, 15 mm. Whilst the tumor volume initially decreased in the 500 V (1000 V/cm) and 700 V (1400 V/cm) groups and subsequently increased, only a transient increase followed by a continuous decrease until the sacrifice was observed in the 900 V (1800 V/cm) group. This result demonstrated a lasting effect of a higher applied voltage on tumor growth inhibition. The histological, immunohistochemical, and western blot findings all confirmed IRE-induced apoptosis in the treatment groups. Taken together, 900 V seemed to be the minimum applied voltage required to reduce tumor growth, though subsequent studies are anticipated to further narrow the voltage intervals and lower the minimum voltage required for tumor inhibition.

Pulse width and intensity effects of pulsed electric fields on cancerous and normal skin cells

Microsecond pulsed electric fields (PEF) have previously been used for various tumour therapies, such as gene therapy, electrochemotherapy and irreversible electroporation (IRE), due to its demonstrated ability. However, recently nanosecond pulsed electric fields (nsPEF) have also been used as a potential tumor therapy via inducing cell apoptosis or immunogenic cell death to prevent recurrence and metastasis by interacting with intracellular organelles. A large proportion of the existing in-vitro studies of nsPEF on cells also suggests cell necrosis and swelling/blebbing can be induced, but the replicability and potential for other effects on cells suggesting a complicated process which requires further investigation. Therefore, this study investigated the effects of pulse width and intensity of nsPEF on the murine melanoma cells (B16) and normal murine fibroblast cells (L929) through electromagnetic simulation and in-vitro experiments. Through examining the evolution patterns of potential difference and electric fields on the intracellular compartments, the simulation has shown a differential effect of nsPEF on normal and cancerous skin cells, which explains well the results observed in the reported experiments. In addition, the modelling has provided a clear evidence that a few hundreds of ns PEF may have caused a mixed mode of effects, i.e. a 'cocktail effect', including cell electroporation and IRE due to an over their threshold voltage induced on the plasma membrane, as well as cell apoptosis and other biological effects caused by its interaction with the intracellular compartments. The in-vitro experiments in the pulse range of the hundreds of nanoseconds showed a possible differential cytotoxicity threshold of electric field intensity between B16 cells and L929 cells.

Lethal Electric Field Thresholds for Cerebral Cells With Irreversible Electroporation and H-FIRE Protocols: An In Vitro Three-Dimensional Cell Model Study

The lethal electric field (LEF) thresholds for three typical cerebral cells, including a malignant glioblastoma (GBM) cell line and two cell lines from the healthy blood-brain barrier (BBB), treated by irreversible electroporation (IRE) or high-frequency irreversible electroporation (H-FIRE) protocols were investigated in an in vitro three-dimensional (3D) cell model. A conventional IRE protocol (90 pulses, 1 Hz, and 100-μs pulse duration) and three novel H-FIRE protocols (1-3-1, 0.5-1-0.5, and 1-1-1) were used to treat the cerebral cells in both 3D single-cell and two-cell models. The electrical conductivity of the 3D cell model under different electric field strengths were characterized with the method of electrochemical impedance spectroscopy (EIS). Based on EIS, a numerical electrothermal model of electroporation was built for the determination of the LEF threshold with different protocols and temperature monitoring. Cell viability was assessed by fluorescence staining 6 h after the treatment. The results showed no thermal lethal effect on cells when these protocols were used. The LEF threshold for GBM cells was significantly lower than that of the healthy BBB cells. These results suggest the possibility of selective ablation of human cerebral GBM by IRE and H-FIRE treatments with no injury or reversible injury to healthy cells, and the potential use of IRE or H-FIRE for transient disruption of the BBB to allow chemotherapy to reach the tumor.

Real-Time Temperature Rise Estimation during Irreversible Electroporation Treatment through State-Space Modeling

To evaluate the feasibility of real-time temperature monitoring during an electroporation-based therapy procedure, a data-driven state-space model was developed. Agar phantoms mimicking low conductivity (LC) and high conductivity (HC) tissues were tested under the influences of high (HV) and low (LV) applied voltages. Real-time changes in impedance, measured by Fourier Analysis SpecTroscopy (FAST) along with the known tissue conductivity and applied voltages, were used to train the model. A theoretical finite element model was used for external validation of the model, producing model fits of 95.8, 88.4, 90.7, and 93.7% at 4 mm and 93.2, 58.9, 90.0, and 90.1% at 10 mm for the HV-HC, LV-LC, HV-LC, and LV-HC groups, respectively. The proposed model suggests that real-time temperature monitoring may be achieved with good accuracy through the use of real-time impedance monitoring.

Establishing electroporation thresholds for targeted cell specific cardiac ablation in a 2D culture model

BACKGROUND

Irreversible electroporation has emerged as a new modality to overcome issues associated with other energy sources for cardiac ablation. Strong evidence on the optimal, effective, and selective voltage threshold is lacking for both in-vitro and pre-clinical in-vivo studies. The aim of this study is to examine the optimal threshold for selective cell ablation on cardiac associated cell types.

METHODS

Conventional monophasic and biphasic pulses of different field strength were delivered in a monolayer culture system of cardiomyocytes, neurons and adipocytes. The dynamics of cell death mechanisms were examined at different time points.

RESULTS

Neurons exhibit higher susceptibility to electroporation and cell death at higher field strength of 1250 V/cm in comparison to cardiomyocytes. Cardiac adipocytes showed lower susceptibility to electroporation in comparison to other cell types. A significant proportion of cardiomyocytes recovered after 24 hours post-electroporation, while neuronal cell death remained consistent but with a significant delayed cell death at a higher voltage threshold. Caspase 3/7 activity was observed in both cardiomyocytes and neurons, with a higher level of activity in cardiomyocytes in response to electroporation. Biphasic and monophasic pulses showed no significant difference in both cell types, and significantly lower cell death in neurons when inter pulse interval was reduced.

CONCLUSIONS

This study presents important findings on the differences in the susceptibility of neurons and cardiomyocytes to IRE. Cell type alone yielded selective and different dynamics in terms of the evolution and signaling mechanism of cell death in response to electroporation. This article is protected by copyright. All rights reserved.

Electroporation Parameters for Human Cardiomyocyte Ablation In Vitro

Cardiac ablation with irreversible electroporation (IRE) is quickly being established as a modality of choice for atrial fibrillation treatment. While it has not yet been optimised, IRE has the potential to significantly limit collateral damage and improve cell-specific targeting associated with other energy sources. However, more tissue and cell-specific evidence is required to demonstrate the selective threshold parameters for human cells. The aim here is to determine the optimal ablation threshold parameters related to lesion size for human cardiomyocytes in 2D culture. Conventional biphasic pulses of different field strengths and on-times were delivered in a monolayer culture system of human AC16 cardiomyocytes. The dynamics of cell death and lesion dimensions were examined at different time points. Human cardiomyocytes are susceptible to significant electroporation and cell death at a field strength of 750 V/cm or higher with 100 μs pulses. Increasing the IRE on-time from 3 ms to 60 ms reduces the effective field threshold to 250 V/cm. Using very short pulses of 2 μs and 5 μs also causes significant cell death, but only at fields higher than 1000 V/cm. A longer on-time results in more cell death and induced greater lesion area in 2D models. In addition, different forms of cell death are predicted based on the evolution of cell death over time. This study presents important findings on the ability of different IRE parameters to induce human cardiomyocyte cell death. Lesion size can be tuned by appropriate choice of IRE parameters and cardiomyocytes display an upregulation of delayed cell death 24 h after electroporation, which is an important consideration for clinical practice.

Open-chest Pulsed Electric Field Ablation of Cardiac Ganglionated Plexi in Acute Canine Models

This study aimed to evaluate the safety and acute effect on markers of cardiac autonomic tone following pulsed electric fields (PEFs) delivered to epicardial ganglionated plexi (GP) during a cardiac surgical procedure. Ablation of GP as a treatment for atrial fibrillation (AF) has shown promise, but thermal ablation energy sources are limited by the risk of inadvertent collateral tissue injury. In acute canine experiments, median sternotomy was performed to facilitate the identification of 5 epicardial GP regions using an anatomy-guided approach. Each site was targeted with saline-irrigated PEF (1000 V, 100 μs, 10 electrocardiogram [ECG]-synchronized pulse sequences). Atrial effective refractory period (AERP) and local electrogram (EGM) amplitude were measured before and after each treatment. Histology was performed on samples from treatment-adjacent structures. In 5 animals, 30 (n = 2) and 60 (n = 3) pulses were successfully delivered to each of the 5 target sites. There was no difference in local atrial EGM amplitude before and after PEF application at each site (1.83 ± 0.41 vs. 1.92 ± 0.53 mV, P = .72). The mean AERP increased from 97 ± 15 ms at baseline to 115 ± 7 ms following treatment at all sites (18.6% increase; 95% confidence interval, 1.9–35.2; P = .037). There were no sustained ventricular arrhythmias or acute evidence of ischemia following delivery. Histology showed complete preservation of adjacent atrial myocardium, phrenic nerves, pericardium, and esophagus. Use of PEF to target regions rich in cardiac GP in open-chest canine experiments was feasible and effective at acutely altering markers of cardiac autonomic tone.

Cardiac ablation with pulsed electric fields: principles and biophysics

Pulsed electric fields (PEFs) have emerged as an ideal cardiac ablation modality. At present numerous clinical trials in humans are exploring PEF as an ablation strategy for both atrial and ventricular arrhythmias, with early data showing significant promise. As this is a relatively new technology there is limited understanding of its principles and biophysics. Importantly, PEF biophysics and principles are starkly different to current energy modalities (radiofrequency and cryoballoon). Given the relatively novel nature of PEFs, this review aims to provide an understanding of the principles and biophysics of PEF ablation. The goal is to enhance academic research and ultimately enable optimization of ablation parameters to maximize procedure success and minimize risk.

High-frequency irreversible electroporation brain tumor ablation: exploring the dynamics of cell death and recovery

Improved therapeutics for malignant brain tumors are urgently needed. High-frequency irreversible electroporation (H-FIRE) is a minimally invasive, nonthermal tissue ablation technique, which utilizes high-frequency, bipolar electric pulses to precisely kill tumor cells. The mechanisms of H-FIRE-induced tumor cell death and potential for cellular recovery are incompletely characterized. We hypothesized that tumor cells treated with specific H-FIRE electric field doses can survive and retain proliferative capacity. F98 glioma and LL/2 Lewis lung carcinoma cell suspensions were treated with H-FIRE to model primary and metastatic brain cancer, respectively. Cell membrane permeability, apoptosis, metabolic viability, and proliferative capacity were temporally measured using exclusion dyes, condensed chromatin staining, WST-8 fluorescence, and clonogenic assays, respectively. Both tumor cell lines exhibited dose-dependent permeabilization, with 1,500 V/cm permitting and 3,000 V/cm inhibiting membrane recovery 24 h post-treatment. Cells treated with 1,500 V/cm demonstrated significant and progressive recovery of apoptosis and metabolic activity, in contrast to cells treated with higher H-FIRE doses. Cancer cells treated with recovery-permitting doses of H-FIRE maintained while those treated with recovery-inhibiting doses lost proliferative capacity. Taken together, our data suggest that H-FIRE induces reversible and irreversible cellular damage in a dose-dependent manner, and the presence of dose-dependent recovery mechanisms permits tumor cell proliferation.

Theoretical model of the influence of irreversibly electroporated cells on post pulse drug delivery to reversibly electroporated cells

This study numerically investigates the drug uptake by a population that includes both reversibly and irreversibly electroporated cells. A theoretical continuum model is developed and simulations are conducted in conditions representing low porosity (cells in tissues) and high porosity (cells in suspension). This model considers only passive diffusion following the electroporation pulse and estimates the permeability increases of reversibly electroporated cells using empirically based predictions that relate the long-lived electropore density to the electric field magnitude. A parametric study investigates whether the permeability and resealing rate of irreversibly electroporated cells influence the delivery to the surviving reversibly electroporated cells. The results show that this influence is negligible when the cell number density is low (cells in dilute suspensions). For conditions of cells in tissue when both the fraction of the total cells that are irreversibly electroporated and the permeability of the irreversibly electroporated cells are high enough, the irreversibly electroporated cells rapidly take up the drug and deplete the extracellular space of the available drug. This lowered extracellular concentration can result in less drug delivery to reversibly electroporated cells.

Improving Prediction of the Potential Distribution Induced by Cylindrical Electrodes within a Homogeneous Rectangular Grid during Irreversible Electroporation

Background: Irreversible electroporation (IRE) is an ablation technique based on the application of short, high-voltage pulses between needle electrodes (diameter: ~1.0 × 10−3 m). A Finite Difference-based software simulating IRE treatment generally uses rectangular grids, yielding discretization issues when modeling cylindrical electrodes and potentially affecting the validity of treatment planning simulations. Aim: Develop an Electric-Potential Estimation (EPE) method for accurate prediction of the electric-potential distribution in the vicinity of cylindrical electrodes. Methods: The electric-potential values in the voxels neighboring the cylindrical electrode voxels were corrected based on analytical solutions derived for coaxial/cylindrical electrodes. Simulations at varying grid resolutions were validated using analytical models. Low-resolution heterogeneous simulations at 2.0 × 10−3 m excluding/including EPE were compared with high-resolution results at 0.25 × 10−3 m. Results: EPE significantly reduced maximal errors compared to analytical results for the electric-potential distributions (26.6–71.8%→0.4%) and for the electrical resistance (30%→1–6%) at 3.0 × 10−3 m voxel-size. EPE significantly improved the mean-deviation (43.1–52.8%→13.0–24.3%) and the calculation-time gain (>15,000×) of low-resolution compared to high-resolution heterogeneous simulations. Conclusions: EPE can accurately predict the potential distribution of neighboring cylindrical electrodes, regardless of size, position, and orientation in a rectangular grid. The simulation time of treatment planning can therefore be shortened by using large voxel-sized models without affecting accuracy of the electric-field distribution, enabling real-time clinical IRE treatment planning.

Experimental and Numerical Investigation of Parameters Affecting High-frequency Irreversible Electroporation for Prostate Cancer Ablation

While the primary goal of focal therapy for prostate cancer (PCa) is conserving patient quality of life by reducing oncological burden, available modalities use thermal energy or whole-gland radiation which can damage critical neurovascular structures within the prostate and increase risk of genitourinary dysfunction. High-frequency irreversible electroporation (H-FIRE) is a promising alternative ablation modality that utilizes bursts of pulsed electric fields (PEFs) to destroy aberrant cells via targeted membrane damage. Due to its non-thermal mechanism, H-FIRE offers several advantages over state-of-the-art treatments, but waveforms have not been optimized for treatment of PCa. In this study, we characterize lethal electric field thresholds (EFTs) for H-FIRE waveforms with three different pulse widths as well as three interpulse delays in vitro and compare them to conventional IRE. Experiments were performed in non-neoplastic and malignant prostate cells to determine the effect of waveforms on both targeted (malignant) and adjacent (non-neoplastic) tissue. A numerical modeling approach was developed to estimate the clinical effects of each waveform including extent of non-thermal ablation, undesired thermal damage, and nerve excitation. Our findings indicate that H-FIRE waveforms with pulse durations of 5 and 10 µs provide large ablations comparable to IRE with tolerable levels of thermal damage and minimized muscle contractions. Lower duration (2 µs) H-FIRE waveforms exhibit the least amount of muscle contractions but require increased voltages which may be accompanied by unwanted thermal damage.

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.

A Brief Insight on Magnetic Resonance Conditional Neurosurgery Robots

The brain is a delicate organ in the human body that requires extreme care. Brain-related diseases are unavoidable. Perse, neurosurgery is a complicated procedure that demands high precision and accuracy. Developing a surgical robot is a complex task. To date, there are only a handful of neurosurgery robots in the market that distinctly undergo clinical procedures. These robots have exorbitant cost that hinders the utmost care progress in the area as they are unaffordable. This paper looked at the historical perspective and presented insight literature of the magnetic resonance conditional stereotactic neurosurgery robots that find their ways in clinics, abandoning research projects and promising research yet to undergo clinical use. In addition, the study also gives a thorough insight into the advantage of magnetic resonance imaging modalities and magnetic resonance conditional robots and the future challenges in automation use. Image compatibility test data and accuracy results are also examined because they guarantee that these systems work correctly in particular imaging settings. The primary differences between these systems include actuation and control technologies, construction materials, and the degree of freedom. Thus, one system has an advantage over the other.

Establishing Irreversible Electroporation Electric Field Potential Threshold in A Suspension In Vitro Model for Cardiac and Neuronal Cells

Aims: Irreversible electroporation is an ablation technique being adapted for the treatment of atrial fibrillation. Currently, there are many differences reported in the in vitro and pre-clinical literature for the effective voltage threshold for ablation. The aim of this study is a direct comparison of different cell types within the cardiovascular system and identification of optimal voltage thresholds for selective cell ablation. Methods: Monophasic voltage pulses were delivered in a cuvette suspension model. Cell viability and live–dead measurements of three different neuronal lines, cardiomyocytes, and cardiac fibroblasts were assessed under different voltage conditions. The immediate effects of voltage and the evolution of cell death was measured at three different time points post ablation. Results: All neuronal and atrial cardiomyocyte lines showed cell viability of less than 20% at an electric field of 1000 V/cm when at least 30 pulses were applied with no significant difference amongst them. In contrast, cardiac fibroblasts showed an optimal threshold at 1250 V/cm with a minimum of 50 pulses. Cell death overtime showed an immediate or delayed cell death with a proportion of cell membranes re-sealing after three hours but no significant difference was observed between treatments after 24 h. Conclusions: The present data suggest that understanding the optimal threshold of irreversible electroporation is vital for achieving a safe ablation modality without any side-effect in nearby cells. Moreover, the evolution of cell death post electroporation is key to obtaining a full understanding of the effects of IRE and selection of an optimal ablation threshold.

Electroporation-Based Therapy for Brain Tumors: A Review

Electroporation-based therapy (EBT), as a high-voltage-pulse technology has been prevalent with favorable clinical outcomes in the treatment of various solid tumors. This review paper aims to promote the clinical translation of EBT for brain tumors. First, we briefly introduced the mechanism of pore formation in a cell membrane activated by external electric fields using a single cell model. Then, we summarized and discussed the current in vitro and in vivo preclinical studies, in terms of (1) the safety and effectiveness of EBT for brain tumors in animal models, and (2) the blood-brain barrier (BBB) disruption induced by EBT. Two therapeutic effects could be achieved in EBT for brain tumors simultaneously, i.e., the tumor ablation induced by irreversible electroporation (IRE) and transient BBB disruption induced by reversible electroporation (RE). The BBB disruption could potentially improve the uptake of antitumor drugs thereby enhancing brain tumor treatment. The challenges that hinder the application of EBT in the treatment of human brain tumors are discussed in the review paper as well.

Modeling methods for treatment planning in overlapping electroporation treatments

OBJECTIVE

Irreversible electroporation (IRE) is a non thermal tissue ablation therapy which is induced by applying high voltage waveforms across electrode pairs. When multiple electrode pairs are sequentially used, the treatment volume (TV) is typically computed as the geometric union of the TVs of individual pairs. However, this method neglects that some regions are exposed to overlapping treatments. Recently, a model describing cell survival probability was introduced which effectively predicted TV with overlapping fields in vivo. However, treatment overlap has yet to be quantified. This study characterizes TV overlap in a controlled in vitro setup with the two existing methods which are compared to an adapted logistic model proposed here.

METHODS

CHO cells were immobilized in agarose gel. Initially, we characterized the electric field threshold and the cell survival probability for overlapping treatments. Subsequently, we created a 2D setup where we compared and validated the accuracy of the different methods in predicting the TV.

RESULTS

Overlap can reduce the electric field threshold required to induce cell death, particularly for treatments with low pulse number. However, it does not have a major impact on TV in the models assayed here, and all the studied methods predict TV with similar accuracy.

CONCLUSION

Treatment overlap has a minor influence in the TV for typical protocols found in IRE therapies.

SIGNIFICANCE

This study provides evidence that the modeling method used in most pre-clinical and clinical studies seems adequate.

Physiological and histopathological effects of electroporation pulse on stomach of rats

BACKGROUND

Irreversible electroporation (IRE) is an emerging tissue ablation technique with widespread potential, especially for cancer treatment. Although the safety and efficacy of IRE for gastric tissue ablation have been demonstrated, there is a gap of knowledge regarding the effect of electroporation pulse (EP) on the physiology and histopathology of the stomach. This study applied EP to the stomach of healthy rats and investigated the digestive function, serum marker levels, and gastric tissue structure of EP-treated rats.

METHODS

Ninety male rats were divided into nine groups and examined up to 28 days post-treatment. A single burst of electroporation pulse (500 V, 99 pluses, 1 Hz, 100 µs) was delivered to the stomachs of rats using a tweezer-style round electrode. Gastric emptying, small intestinal transit, and gastric secretion were measured to evaluate the digestive function. Serum marker levels were determined using ELISA. Haematoxylin-eosin, Masson trichrome, and immunofluorescence were performed for histopathological analysis.

RESULTS

No  significant effect on gastric emptying or secretion was found post-EP, whereas the small intestinal transit decreased at 4 h and rapidly recovered to normal on 1-day post-EP. Further, serum TNF-α and IL-1β levels temporarily changed during the acute phase but returned to baseline within 28 days. Moreover, histopathological analysis revealed that cell death occurred immediately post-EP in the ablation area, whereas the gastric wall scaffold in the ablation region remained intact post-EP.

CONCLUSIONS

This study demonstrates the safety and efficacy of EP on the physiology and histopathology of the stomach and lays a foundation for more comprehensive applications of this technique.

Dynamic Electroporation Model Evaluation on Rabbit Tissues

Biological electroporation is a process of opening pores in the cell membrane when exposed to intense electric fields. This work provides results for validation of a dynamic model of electroporation on biological tissues. Computational simulations were carried out and results for the electrical current through the tissue and increase of the tissue temperature were compared to experimental results. Two calculation methods were used: Equivalent Circuit Method and Finite Element Method. With Equivalent Circuit Method the dielectric dispersion present in biological tissues was included. Liver, kidney and heart of rabbit were used in the experiments. Voltage pulse protocols and voltage ramps were applied using stainless steel needles electrodes. There is good agreement between the simulated and experimental results with mean errors below 15%, with the simulated results within the experimental standard deviation. Only for the protocol with fundamental frequency of 50 kHz, the simulation performed by the Finite Element Method using a commercial software did not correctly represent the current, with errors reaching 50%. The justification for the error found is due to the dielectric dispersion that was not included in this simulator.

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.

Irreversible Electroporation and Nivolumab Combined with Intratumoral Administration of a Toll-Like Receptor Ligand, as a Means of In Vivo Vaccination for Metastatic Pancreatic Ductal Adenocarcinoma (PANFIRE-III). A Phase-I Study Protocol

Simple Summary

Metastatic pancreatic ductal adenocarcinoma has a dismal prognosis, and to date no curative treatment options exist. The image guided tumor ablation technique irreversible electroporation (IRE) employs high-voltage electrical pulses through the application of several needle electrodes in and around the tumor in order to induce cell death. IRE ablation of the primary tumor has the ability to reduce pancreatic tumor induced immune suppression while allowing the expansion of tumor specific effector T cells, hereby possibly shifting the pancreatic tumor microenvironment into a more immune permissive state. The addition of immune enhancing therapies to IRE might work synergistically and could potentially induce a clinically significant treatment effect. This study protocol describes the rationale and design of the PANFIRE-III trial that aims to assess the safety of the combination of IRE with IMO-2125 (toll-like receptor 9 ligand) and/or nivolumab in patients with metastatic pancreatic ductal adenocarcinoma.

Abstract

Irreversible electroporation (IRE) is a novel image-guided tumor ablation technique with the ability to generate a window for the establishment of systemic antitumor immunity. IRE transiently alters the tumor’s immunosuppressive microenvironment while simultaneously generating antigen release, thereby instigating an adaptive immune response. Combining IRE with immunotherapeutic drugs, i.e., electroimmunotherapy, has synergistic potential and might induce a durable antitumor response. The primary objective of this study is to assess the safety of the combination of IRE with IMO-2125 (a toll-like receptor 9 ligand) and/or nivolumab in patients with metastatic pancreatic ductal adenocarcinoma (mPDAC). In this randomized controlled phase I clinical trial, 18 patients with mPDAC pretreated with chemotherapy will be enrolled in one of three study arms: A (control): nivolumab monotherapy; B: percutaneous IRE of the primary tumor followed by nivolumab; or C: intratumoral injection of IMO-2125 followed by percutaneous IRE of the primary tumor and nivolumab. Assessments include contrast enhanced computed tomography (ceCT), ¹⁸F-FDG and ¹⁸F-BMS-986192 (PD-L1) positron emission tomography (PET)-CT, biopsies of the primary tumor and metastases, peripheral blood samples, and quality of life and pain questionnaires. There is no curative treatment option for patients with mPDAC, and palliative chemotherapy regimens only moderately improve survival. Consequently, there is an urgent need for innovative and radically different treatment approaches. Should electroimmunotherapy establish an effective and durable anti-tumor response, it may ultimately improve PDAC’s dismal prognosis.

Generation of Tumor-activated T cells using electroporation

Expansion of cytotoxic T lymphocytes (CTLs) is a crucial step in almost all cancer immunotherapeutic methods. Current techniques for expansion of tumor-reactive CTLs present major limitations. This study introduces a novel method to effectively produce and expand tumor-activated CTLs using high-voltage pulsed electric fields. We hypothesize that utilizing high-voltage pulsed electric fields may be an ideal method to activate and expand CTLs due to their non-thermal celldeath mechanism. Tumor cells were subjected to high-frequency irreversible electroporation (HFIRE) with various electric field magnitudes (1250, 2500 V/cm) and pulse widths (1, 5, and 10 µs), or irreversible electroporation (IRE) at 1250 V/cm. The treated tumor cells were subsequently cocultured with CD4+ and CD8+ T cells along with antigen-presenting cells. We show that tumor-activated CTLs can be produced and expanded when exposed to treated tumor cells. Our results suggest that CTLs are more effectively expanded when pulsed with HFIRE conditions that induce significant cell death (longer pulse widths and higher voltages). Activated CD8+ T cells demonstrate cytotoxicity to untreated tumor cells suggesting effector function of the activated CTLs. The activated CTLs produced with our technique could be used for clinical applications with the goal of targeting and eliminating the tumor.

An in vivo study of a custom-made high-frequency irreversible electroporation generator on different tissues for clinically relevant ablation zones

PURPOSE

To examine the ablation zone, muscle contractions, and temperature increases in both rabbit liver and kidney models in vivo for a custom-made high-frequency irreversible electroporation (H-FIRE) generator.

MATERIALS AND METHODS

A total of 18 New Zealand white rabbits were used to investigate five H-FIRE protocols (n = 3 for each protocol) and an IRE protocol (n = 3) for the performance of the designed H-FIRE device in both liver and kidney tissues. The ablation zone was determined by using histological analysis 72 h after treatment. The extent of muscle contractions and temperature change during the application of pulse energy were measured by a commercial accelerometer attached to animals and fiber optic temperature probe inserted into organs with IRE electrodes, respectively.

RESULTS

All H-FIRE protocols were able to generate visible ablation zones without muscle contractions, for both liver and kidney tissues. The area of ablation zone generated in H-FIRE pulse protocols (e.g., 0.3-1 μs, 2000 V, and 90-195 bursts) appears similar to that of IRE protocol (100 μs, 1000 V, and 90 pulses) in both liver and kidney tissues. No significant temperature increase was noticed except for the protocol with the highest pulse energy (e.g., 1 μs, 2000 V, and 180 bursts).

CONCLUSION

Our work serves to complement the current H-FIRE pulse waveforms, which can be optimized to significantly improve the quality of ablation zone in terms of precision for liver and kidney tumors in clinical setting.

Comparison between high-frequency irreversible electroporation and irreversible electroporation ablation of small swine liver: follow-up of DCE-MRI and pathological observations

Background:

High-frequency irreversible electroporation (H-FIRE) is a novel, next-generation nanoknife technology with the advantage of relieving irreversible electroporation (IRE)-induced muscle contractions. However, the difference between IRE and H-FIRE with distinct ablation parameters was not clearly defined. This study aimed to compare the efficacy of the two treatments in vivo.

Methods:

Ten Bama miniature swine were divided into two group: five in the 1-day group and five in the 7-day group. The efficacy of IRE and H-FIRE ablation was compared by volume transfer constant (Krans), rate constant (Kep) and extravascular extracellular volume fraction (Ve) value of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), size of the ablation zone, and histologic analysis. Each animal underwent the IRE and H-FIRE. Temperatures of the electrodes were measured during ablation. DCE-MRI images were obtained 1, 4, and 7 days after ablation in the 7-day group. All animals in the two groups were euthanized 1 day or 7 days after ablation, and subsequently, IRE and H-FIRE treated liver tissues were collected for histological examination. Student's t test or Mann-Whitney U test was applied for comparing any two groups. One-way analysis of variance (ANOVA) test and Welch's ANOVA test followed by Holm-Sidak's multiple comparisons test, one-way ANOVA with repeated measures followed by Bonferroni test, or Kruskal-Wallis H test followed by Dunn's multiple comparison test was used for multiple group comparisons and post hoc analyses. Pearson correlation coefficient test was conducted to analyze the relationship between two variables.

Results:

Higher Ve was seen in IRE zone than in H-FIRE zone (0.14 ± 0.02 vs. 0.08 ± 0.05, t = 2.408, P = 0.043) on day 4, but no significant difference was seen in Ktrans or Kep between IRE and H-FIRE zones at all time points (all P > 0.05). For IRE zone, the greatest Ktrans was seen on day 7, which was significantly higher than that on day 1 (P = 0.033). The ablation zone size of H-FIRE was significantly larger than IRE 1 day (4.74 ± 0.88 cm²vs. 3.20 ± 0.77 cm², t = 3.241, P = 0.009) and 4 days (2.22 ± 0.83 cm²vs. 1.30 ± 0.50 cm², t = 2.343, P = 0.041) after treatment. Apoptotic index (0.05 ± 0.02 vs. 0.73 ± 0.06 vs. 0.68 ± 0.07, F = 241.300, P < 0.001) and heat shock protein 70 (HSP70) (0.03 ± 0.01 vs. 0.46 ± 0.09 vs. and 0.42 ± 0.07, F = 64.490, P < 0.001) were significantly different between the untreated, IRE and H-FIRE zones, but no significant difference was seen in apoptotic index or HSP70 between IRE and H-FIRE zone (both P > 0.05). Electrode temperature variations were not significantly different between the two zones (18.00 ± 3.77°C vs. 16.20 ± 7.45°C, t = 0.682, P = 0.504). The Ktrans value (r = 0.940, P = 0.017) and the Kep value (r = 0.895, P = 0.040) of the H-FIRE zone were positively correlated with the number of hepatocytes in the ablation zone.

Conclusions:

H-FIRE showed a comparable ablation effect to IRE. DCE-MRI has the potential to monitor the changes of H-FIRE ablation zone.

Cell death due to electroporation - A review

Exposure of cells to high voltage electric pulses increases transiently membrane permeability through membrane electroporation. Electroporation can be reversible and is used in gene transfer and enhanced drug delivery but can also lead to cell death. Electroporation resulting in cell death (termed as irreversible electroporation) has been successfully used as a new non-thermal ablation method of soft tissue such as tumours or arrhythmogenic heart tissue. Even though the mechanisms of cell death can influence the outcome of electroporation-based treatments due to use of different electric pulse parameters and conditions, these are not elucidated yet. We review the mechanisms of cell death after electroporation reported in literature, cell injuries that may lead to cell death after electroporation and membrane repair mechanisms involved. The knowledge of membrane repair and cell death mechanisms after cell exposure to electric pulses, targets of electric field in cells need to be identified to optimize existing and develop of new electroporation-based techniques used in medicine, biotechnology, and food technology.