Implications and considerations of thermal effects when applying irreversible electroporation tissue ablation therapy

Electrolysis products, reactive oxygen species and ATP loss contribute to cell death following irreversible electroporation with microsecond-long pulsed electric fields

Membrane permeabilization and thermal injury are the major cause of cell death during irreversible electroporation (IRE) performed using high electric field strength (EFS) and small number of pulses. In this study, we explored cell death under conditions of reduced EFS and prolonged pulse application, identifying the contributions of electrolysis, reactive oxygen species (ROS) and ATP loss. We performed ablations with conventional high-voltage low pulse (HV-LP) and low-voltage high pulse (LV-HP) conditions in a 3D tumor mimic, finding equivalent ablation volumes when using 2000 V/cm 90 pulses or 1000 V/cm 900 pulses respectively. These results were confirmed by performing ablations in swine liver. In LV-HP treatment, ablation volume was found to increase proportionally with pulse numbers, without the substantial temperature increase seen with HV-LP parameters. Peri-electrode pH changes, ATP loss and ROS production were seen in both conditions, but LV-HP treatments were more sensitive to blocking of these forms of cell injury. Increases in current drawn during HV-LP was not observed during LV-HP condition where the total ablation volume correlated to the charge delivered into the tissue which was greater than HV-LP treatment. LV-HP treatment provides a new paradigm in using pulsed electric fields for tissue ablation with clinically relevant volumes.

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.

Tumor location on electroporation therapies by means of multi-electrode structures and machine learning

Electroporation is a phenomenon produced in the cell membrane when it is exposed to high pulsed electric fields that increases its permeability. Among other application fields, this phenomenon can be exploited in a clinical environment for tumor ablation therapies. In this context to achieve optimum results, it is convenient to focus the treatment on the tumor tissue to minimize side effects. In this work, a pre-treatment tumor location method is developed, with the purpose of being able to precisely target the therapy. This is done by taking different impedance measurements with a multi-output electroporation generator in conjunction with a multi-electrode structure. Data are processed by means of a vector of independent artificial neural networks, trained and tested with simulation data, and validated with phantom gels. This algorithm proved to provide suitable accuracy in spite of the low electrode count compared to the number of electrodes of a standard electrical impedance tomography device.

Characteristics of pulsed electric field cardiac ablation porcine treatment zones with a focal catheter

OBJECTIVES

Pulsed electric field (PEF) therapies employ punctuated energy delivery to kill cells in a volume of tissue through mechanisms that are not dependent on thermal processes. A key component to successful cardiac ablation procedures is ensuring the generation of transmural, contiguous ablation zones, which requires in-depth knowledge regarding treatment sizes for a given therapeutic application.

METHODS

In this study, a series of acute treatments were delivered to porcine ventricles, where triphenyl tetrazolium chloride (TTC) vitality stain was used to identify treatment effect sizes for the three focal monopolar CENTAURI PEF cardiac ablation energy settings.

RESULTS

Treatment depths were 5.7, 7.2, and 8.2 mm for the 19, 22, and 25 A energy settings, respectively. Gross pathology indicated umbral zones of hemorrhage surrounded by pale avital TTC-negative-negative tissue, which contrasted significantly from radiofrequency ablation (RF) controls. Histologically, treatment zones are identified by regions of contraction band necrosis and cardiomyocytolysis, which contrasted with RF control lesions composed primarily of coagulation necrosis.

CONCLUSIONS

Together, these data indicate the ability for focal monopolar PEF treatments to generate deep treatment zones in cardiac ablation without incurring the gross or histological coagulative characteristics of RF thermal lesions.

Palliative Treatment of Esophageal Cancer Using Calcium Electroporation

Simple Summary

Calcium electroporation is a new cancer therapy wherein a high, rapid influx of calcium, facilitated by electrical pulses, is used to kill cancer cells. This pilot study aimed to evaluate the safety and feasibility of this new treatment for patients with non-curable esophageal cancer. The treatment was administrated during an endoscopic examination, under general anesthesia, and in an outpatient setting. Eight patients were treated. One severe adverse event occurred (requiring a single blood transfusion) and another three mild side effects were seen. Two patients reported dysphagia relief after treatment and one patient had a partial response evaluated by CT. Six months after treatment, the same patient was still in good condition, without the need for further treatment. Calcium electroporation was conducted in eight patients with only a few side effects. More studies are warranted to evaluate clinical efficacy.

Abstract

Calcium electroporation (CaEP) is a novel cancer therapy wherein high intracellular calcium levels, facilitated by reversible electroporation, trigger tumor necrosis. This study aimed to establish safety with CaEP within esophageal cancer. Patients with non-curable esophageal cancer were included at Copenhagen University Hospital Rigshospitalet in 2021 and 2022. In an outpatient setting, calcium gluconate was injected intratumorally followed by reversible electroporation applied with an endoscopic electrode. The primary endpoint was the prevalence of adverse events, followed by palliation of dysphagia. All patients were evaluated with CT and upper endoscopies up to two months after treatment. The trial was registered at ClinicalTrials.gov (NCT04958044). Eight patients were treated. One serious adverse event (anemia, requiring a single blood transfusion) and three adverse events (mild retrosternal pain (two) and oral thrush (one)) were registered. Initially, six patients suffered from dysphagia: two reported dysphagia relief and four reported no change. From the imaging evaluation, one patient had a partial response, three patients had no response, and four patients had progression. Six months after treatment, the patient who responded well was still in good condition and without the need for further oncological treatment. CaEP was conducted in eight patients with only a few side effects. This study opens the way for larger studies evaluating tumor regression and symptom palliation.

Multimodal therapy with or without irreversible electroporation for unresectable locally advanced pancreatic adenocarcinoma: a systematic review and meta-analysis

BACKGROUND

Irreversible electroporation (IRE) is used as a locoregional treatment modality for patients with locally advanced pancreatic cancer (LAPC), but is non-curative and is associated with postoperative morbidity and mortality. We performed a systematic review and meta-analysis comparing survival outcomes of multimodal therapy with or without IRE.

METHODS

Separate searches were performed for multimodal therapy + IRE and multimodal therapy alone given the lack of comparative literature using PubMed, SCOPUS, and Cochrane Library in 3/2021. We determined overall survival (OS) and progression-free survival (PFS) from diagnosis and time of IRE. Treatment-related morbidity and mortality was determined.

RESULTS

Of 585 published articles, 48 met inclusion criteria for IRE (n = 27) and without IRE (n = 21) with data for 1420 (IRE) and 1348 (without IRE) patients. The 6/12/24 months OS with IRE was 99%/84%/28%. The 6/12/24 months OS without IRE was 99%/80%/12%. At 12 months from IRE, OS was 55% and PFS was 12%. The mean major complication and 90-day mortality rates for IRE were 17.95% and 2.65%.

CONCLUSION

Multimodal therapy alone is associated with similar OS to multimodal therapy + IRE in patients with LAPC. Most patients progress and nearly half die within 1 year of the IRE procedure. Given the lack of quality prospective data, IRE should remain experimental and be used with caution in LAPC.

Primer on Pulsed Electrical Field Ablation: Understanding the Benefits and Limitations

Pulsed electrical field (PEF) energy is a promising technique for catheter ablation of cardiac arrhythmias. In this article, the key aspects that need to be considered for safe and effective PEF delivery are reviewed, and their impact on clinical feasibility is discussed. The most important benefit of PEF appears to be the ability to kill cells through mechanisms that do not alter stromal proteins, sparing sensitive structures to improve safety, without sacrificing cardiomyocyte ablation efficacy. Many parameters affect PEF treatment outcomes, including pulse intensity, waveform shape, and number of pulses, as well as electrode configuration and geometry. These physical and electrical characteristics must be titrated carefully to balance target tissue effects with collateral implications (muscle contraction, temperature rise, risk of electrical arcing events). It is important to note that any combination of parameters affecting PEF needs to be tested for clinical efficacy and safety. Applying PEF clinically requires knowledge of the fundamentals of this technology to exploit its opportunities and generate viable, durable health improvements for patients.

Determining tissue conductivity in tissue ablation by nanosecond pulsed electric fields

Nanosecond pulsed electric field (nsPEF) causes the permeabilization of the cell membrane and has been used to non-thermally treat cancerous tissues. As increased permeabilization in membranes were reported to be accompanied by impedance changes, the ablation effect of nsPEF on tissues can be monitored via the changes in tissue conductivity. In this study, effects of nsPEF on biological tissues were evaluated by determining the conductivities of potato and 4 T1-luc breast tumor tissues ex vivo from a murine model subjected to multiple 100-ns, 1-10 kV pulses. Using a four-needle electrode system with a calibrated electrode constant of 1.1 ± 0.1 cm, the conductivities of tissues was determined from both the network-analyzer measurement, before and after treatment, and voltage-current measurement in real-time. The conductivity of the potato tissue was measured for a frequency range of 0.1-3 MHz, and it increased with increasing pulse number and voltage amplitude. The conductivity of the tumor tissue was also observed to increase with pulse number and pulse voltage over a similar frequency range. In addition, the linear correlation between the ablation area in a treated potato tissue and the conductivity change in the tissue suggests that conductivity analysis of biological tissue under treatment could be a fast and sensitive approach to evaluate the effectiveness of a nsPEF treatment.

Lung Ablation with Irreversible Electroporation Promotes Immune Cell Infiltration by Sparing Extracellular Matrix Proteins and Vasculature: Implications for Immunotherapy

Background: This study investigated the sparing of the extracellular matrix (ECM) and blood vessels at the site of lung irreversible electroporation (IRE), and its impact on postablation T cell and macrophage populations. Materials and Methods: Normal swine (n = 8) lung was treated with either IRE or microwave ablation (MWA), followed by sacrifice at 2 and 28 days (four animals/timepoint) after treatment. En bloc samples of ablated lung were stained for blood vessels (CD31), ECM proteins (Collagen, Heparan sulfate, and Decorin), T cells (CD3), and macrophages (Iba1). Stained slides were analyzed with an image processing software (ImageJ) to count the number of positive staining cells or the percentage area of tissue staining for ECM markers, and the statistical difference was evaluated with Student's t-test. Results: Approximately 50% of the blood vessels and collagen typically seen in healthy lung were evident in IRE treated samples at Day 2, with complete destruction within MWA treated lung. These levels increased threefold by Day 28, indicative of post-IRE tissue remodeling and regeneration. Decorin and Heparan sulfate levels were reduced, and it remained so through the duration of observation. Concurrently, numbers of CD3⁺ T cells and macrophages were not different from healthy lung at Day 2 after IRE, subsequently increasing by 2.5 and 1.5-fold by Day 28. Similar findings were restricted to the peripheral inflammatory rim of MWA samples, wherein the central necrotic regions remained acellular through Day 28. Conclusion: Acute preservation of blood vessels and major ECM components was observed in IRE treated lung at acute time points, and it was associated with the increased infiltration and presence of T cells and macrophages, features that were spatially restricted in MWA treated lung.

Histotripsy Ablation Alters the Tumor Microenvironment and Promotes Immune System Activation in a Subcutaneous Model of Pancreatic Cancer

Pancreatic cancer is a significant cause of cancer-related deaths in the United States with an abysmal five-year overall survival rate that is under 9%. Reasons for this mortality include the lack of late-stage treatment options and the immunosuppressive tumor microenvironment. Histotripsy is an ultrasound-guided, noninvasive, nonthermal tumor ablation therapy that mechanically lyses targeted cells. To study the effects of histotripsy on pancreatic cancer, we utilized an in vitro model of pancreatic adenocarcinoma and compared the release of potential antigens following histotripsy treatment to other ablation modalities. Histotripsy was found to release immune-stimulating molecules at magnitudes similar to other nonthermal ablation modalities and superior to thermal ablation modalities, which corresponded to increased innate immune system activation in vivo. In subsequent in vivo studies, murine Pan02 tumors were grown in mice and treated with histotripsy. Flow cytometry and rtPCR were used to determine changes in the tumor microenvironment over time compared to untreated animals. In mice with pancreatic tumors, we observed significantly increased tumor-progression-free and general survival, with increased activation of the innate immune system 24 h posttreatment and decreased tumor-associated immune cell populations within 14 days of treatment. This study demonstrates the feasibility of using histotripsy for pancreatic cancer ablation and provides mechanistic insight into the initial innate immune system activation following treatment. Further work is needed to establish the mechanisms behind the immunomodulation of the tumor microenvironment and immune effects.

Feasibility and effectiveness of endoscopic irreversible electroporation for the upper gastrointestinal tract: an experimental animal study

Irreversible electroporation (IRE) is a local non-thermal ablative technique currently used to treat solid tumors. Here, we investigated the clinical potency and safety of IRE with an endoscope in the upper gastrointestinal tract. Pigs were electroporated with recently designed endoscopic IRE catheters in the esophagus, stomach, and duodenum. Two successive strategies were introduced to optimize the electrical energy for the digestive tract. First, each organ was electroporated and the energy upscaled to confirm the upper limit energy inducing improper tissue results, including bleeding and perforation. Excluding the unacceptable energy from the first step, consecutive electroporations were performed with stepwise reductions in energy to identify the energy that damaged each layer. Inceptive research into inappropriate electrical intensity contributed to extensive hemorrhage and bowel perforation for each tissue above a certain energy threshold. However, experiments performed below the precluded energy accompanying hematoxylin and eosin staining and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays showed that damaged mucosal area and depth significantly decreased with decreased energy. Relevant histopathology showed infiltration of inflammatory cells with pyknotic nuclei at the electroporated lesion. This investigation demonstrated the possibility of endoscopic IRE in mucosal dysplasia or early malignant tumors of the hollow viscus.

Predictors of Occlusion of Hepatic Blood Vessels after Irreversible Electroporation of Liver Tumors

PURPOSE

To examine predictors of midterm occlusion in portal and hepatic veins within or adjacent to the ablation zone after irreversible electroporation (IRE) of liver tumors.

MATERIALS AND METHODS

This retrospective cohort analysis included 39 patients who underwent CT-guided IRE of liver tumors. Vessels within or adjacent to the ablation zone were identified on CT images acquired immediately after the procedure, and the positional relationships with the ablation zone (within/adjacent), locations (proximal/distal), and diameters (< 4 mm or ≥ 4 mm) were evaluated. Using contrast-enhanced follow-up scans, each vessel was classified as patent, stenosed, or occluded. Associations between vessel occlusion and each variable were investigated.

RESULTS

Overall, 33 portal veins and 64 hepatic veins were analyzed. Follow-up scans showed occlusion in 12/33 (36.7%) portal veins and 17/64 (26.6%) hepatic veins. Vessels within the ablation zone were occluded significantly more frequently than vessels adjacent to the ablation zone (portal: 55.6% [10/18] vs 13.3% [2/15], P = .04; hepatic: 45.4% [15/33] vs 6.4% [2/31], P = .011). Vessels with a diameter < 4 mm were also occluded significantly more frequently than vessels with a diameter ≥ 4 mm (portal: 72.7% [8/11] vs 18.1% [4/22], P = .011; hepatic: 54.8% [17/31] vs 0% [0/33], P < .001). The respective positive and negative predictive values for occlusion of vessels categorized as both within and < 4 mm were 88% (7/8) and 82% (20/25) for portal veins and 79% (15/19) and 96% (43/45) for hepatic veins.

CONCLUSIONS

Midterm vessel occlusion after liver IRE could be predicted with relatively high accuracy by assessing ablation location and vessel diameter.

Effect of irreversible electroporation parameters and the presence of a metal stent on the electric field line pattern

The final ablation zone created with irreversible electroporation (IRE) depends on the size, shape and strength of the electric field that is influenced by several parameters. A profound understanding of the effect of IRE parameter alterations on the electric field are a prerequisite for a safe and effective treatment. Here, we demonstrate a semolina in castor oil model that enables visualization of the static electric field developed by a high-voltage generator between two needle-electrodes. We intuitively visualize the variation in electric field line pattern for selected IRE parameters; active needle length, inter-needle distance, applied voltage and presence of a nearby metal stent, by cameras in three dimensions. The observations were compared to and supported by two-dimensional numerical simulations of the electric field. Our semolina model visualizes the disturbance of the electric field by a metal stent, potentially leading to an incomplete tumour ablation between the needles. The reduction in electric field strength and the area at risk for incomplete tumour ablation are confirmed by the numerical simulations. The semolina model provides insight in the fundamental physics of the electric field, the effect of alterations in IRE parameter combinations and presence of a metal stent within the ablation zone.

Starting a Fire Without Flame: The Induction of Cell Death and Inflammation in Electroporation-Based Tumor Ablation Strategies

New therapeutic strategies and paradigms are direly needed for the treatment of cancer. While the surgical removal of tumors is favored in most cancer treatment plans, resection options are often limited based on tumor localization. Over the last two decades, multiple tumor ablation strategies have emerged as promising stand-alone or combination therapeutic options for patients. These strategies are often employed to treat tumors in areas where surgical resection is not possible or where chemotherapeutics have proven ineffective. The type of cell death induced by the ablation modality is a critical aspect of therapeutic success that can impact the efficacy of the treatment and systemic anti-tumor immune system responses. Electroporation-based ablation technologies include electrochemotherapy, irreversible electroporation, and other modalities that rely on pulsed electric fields to create pores in cell membranes. These pores can either be reversible or irreversible depending on the electric field parameters and can induce cell death either alone or in combination with a therapeutic agent. However, there have been many controversial findings among these technologies as to the cell death type initiated, from apoptosis to pyroptosis. As cell death mechanisms can impact treatment side effects and efficacy, we review the main types of cell death induced by electroporation-based treatments and summarize the impact of these mechanisms on treatment response. We also discuss potential reasons behind the variability of findings such as the similarities between cell death pathways, differences between cell-types, and the variation in electric field strength across the treatment area.

Irreversible Electroporation for Locally Advanced Pancreatic Cancer

Several minimally invasive image guided tumor ablation techniques have been added to the treatment spectrum for locally advanced pancreatic cancer (LAPC). Irreversible electroporation (IRE) might have a significant additive value in the management of this difficult-to-treat disease. As opposed to thermal ablative techniques, IRE induces cell death by the delivery of high-voltage electrical pulses. The electrical energy disrupts the cellular membrane integrity, causes loss of cellular homeostasis and ultimately results in cell death. The extracellular matrix of connective tissue in surrounding delicate structures such as bile ducts, bowel wall, and larger blood vessels is spared. The preservation of these structures makes IRE attractive for the treatment of pancreatic cancers that are unresectable due to their anatomical location (ie, LAPC and local recurrence after surgical resection). In addition to its cytoreductive abilities, evidence is emerging on IRE's capability to induce systemic immunomodulation through active in vivo vaccination against pancreatic cancer cells. These effects in combination with immunotherapy may offer a new treatment paradigm for tumors with low immunogenic potential like pancreatic ductal adenocarcinoma (PDAC). This review discusses several practical and technical issues of IRE for LAPC: clinical evaluation, indications, patient preparations, procedural steps, imaging characteristics, clinical results, and "tricks of the trade" used to improve the safety and efficacy of the treatment. Future directions such as the combination of IRE with immunotherapy will be shortly addressed.

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.

Pre-clinical investigation of the synergy effect of interleukin-12 gene-electro-transfer during partially irreversible electropermeabilization against melanoma

BACKGROUND

Melanoma is a very aggressive skin tumor that can be cured when diagnosed and treated in its early stages. However, at the time of identification, the tumor is frequently in a metastatic stage. Intensive research is currently ongoing to improve the efficacy of the immune system in eliminating cancer cells. One approach is to boost the activation of cytotoxic T cells by IL-12 cytokine that plays a central role in the activation of the immune system. In parallel, physical methods such as electropermeabilization-based treatments are currently under investigation and show promising results.

METHODS

In this study, we set electrical parameters to induce a partial-irreversible electropermeabilization (pIRE) of melanoma to induce a sufficient cell death and potential release of tumor antigens able to activate immune cells. This protocol mimics the situation where irreversible electropermeabilization is not fully completed. Then, a peritumoral plasmid IL-12 electrotransfer was combined with pIRE treatment. Evaluation of the tumor growth and survival was performed in mouse strains having a different immunological background (C57Bl/6 (WT), nude and C57Bl6 (TLR9-/-)).

RESULTS

pIRE treatment induced apoptotic cell death and a temporary tumor growth delay in all mouse strains. In C57Bl/6 mice, we showed that peritumoral plasmid IL-12 electrotransfer combined with tumor pIRE treatment induced tumor regression correlating with a local secretion of IL-12 and IFN-γ. This combined treatment induced a growth delay of distant tumors and prevented the emergence of a second tumor in 50% of immunocompetent mice.

CONCLUSIONS

The combination of pIL-12 GET and pIRE not only enhanced survival but could bring a curative effect in wild type mice. This two-step treatment, named Immune-Gene Electro-Therapy (IGET), led to a systemic activation of the adaptive immune system and the development of an anti-tumor immune memory.

Electric field-responsive nanoparticles and electric fields: physical, chemical, biological mechanisms and therapeutic prospects

Electric fields are among physical stimuli that have revolutionized therapy. Occurring endogenously or exogenously, the electric field can be used as a trigger for controlled drug release from electroresponsive drug delivery systems, can stimulate wound healing and cell proliferation, may enhance endocytosis or guide stem cell differentiation. Electric field pulses may be applied to induce cell fusion, can increase the penetration of therapeutic agents into cells, or can be applied as a standalone therapy to ablate tumors. This review describes the main therapeutic trends and overviews the main physical, chemical and biological mechanisms underlying the actions of electric fields. Overall, the electric field can be used in therapeutic approaches in several ways. The electric field can act on drug carriers, cells and tissues. Understanding the multiple effects of this powerful tool will help harnessing its full therapeutic potential in an efficient and safe way.

Conductivity Rise During Irreversible Electroporation: True Permeabilization or Heat?

Purpose

Irreversible electroporation (IRE) induces apoptosis with high-voltage electric pulses. Although the working mechanism is non-thermal, development of secondary Joule heating occurs. This study investigated whether the observed conductivity rise during IRE is caused by increased cellular permeabilization or heat development.

Methods

IRE was performed in a gelatin tissue phantom, in potato tubers, and in 30 patients with unresectable colorectal liver metastases (CRLM). Continuous versus sequential pulsing protocols (10-90 vs. 10-30-30-30) were assessed. Temperature was measured using fiber-optic probes. After temperature had returned to baseline, 100 additional pulses were delivered. The primary technique efficacy of the treated CRLM was compared to the periprocedural current rise. Seven patients received ten additional pulses after a 10-min cool-down period.

Results

Temperature and current rise was higher for the continuous pulsing protocol (medians, gel: 13.05 vs. 9.55 °C and 9 amperes (A) vs. 7A; potato: 12.70 vs. 10.53 °C and 6.0A vs. 6.5A). After cooling-down, current returned to baseline in the gel phantom and near baseline values (Δ2A with continuous- and Δ5A with sequential pulsing) in the potato tubers. The current declined after cooling-down in all seven patients with CRLM, although baseline values were not reached. There was a positive correlation between current rise and primary technique efficacy (p = 0.02); however, the previously reported current increase threshold of 12–15A was reached in 13%.

Conclusion

The observed conductivity rise during IRE is caused by both cellular permeabilization and heat development. Although a correlation between current rise and efficacy exists, the current increase threshold seems unfeasible for CRLM.

Electronic supplementary material

The online version of this article (10.1007/s00270-018-1971-7) contains supplementary material, which is available to authorized users.

Focal Therapy in Primary Localised Prostate Cancer: The European Association of Urology Position in 2018

Radical treatment of localised prostate cancer is recognised to be an unnecessary intervention or overtreatment in many men. Consequently, there has been a rapid uptake in the use of focal ablative therapies. However, there are several biological and practical concerns about such approaches as they have yet to be proved as robust treatment options. In particular, the multifocal nature of prostate cancer argues against unifocal treatment, while limitations in imaging can preclude the accurate identification of the number, location, and extent of prostate cancer foci. To date, a number of ablative options have reported results on mainly low-risk disease. Most series are relatively immature, with a lack of consistent follow-up, and the morbidity of retreatment is often not considered. The authors consider focal therapy to be an investigational modality, and encourage prospective recording of outcomes and recruitment of suitable patients.

PATIENT SUMMARY

Focal therapy of prostate cancer is the targeted destruction of cancer within a specific part of the prostate gland, sparing the rest of the prostate and nearby tissue. This procedure could potentially reduce side effects when compared with established standard treatments, such as surgery or radiotherapy, which treat the entire prostate. Studies show that for most men with low-risk cancer, active surveillance is the preferred treatment option. However, the available data regarding all forms of focal therapy are still poor and inconclusive. Consequently, due to both the lack of clear results associated with focal therapy and the difficulties in detecting all cancerous areas of the prostate, focal therapy should be considered an investigational modality only.

Characterization of Cell Membrane Permeability In Vitro Part II: Computational Model of Electroporation-Mediated Membrane Transport

Electroporation is the process by which applied electric fields generate nanoscale defects in biological membranes to more efficiently deliver drugs and other small molecules into the cells. Due to the complexity of the process, computational models of cellular electroporation are difficult to validate against quantitative molecular uptake data. In part I of this two-part report, we describe a novel method for quantitatively determining cell membrane permeability and molecular membrane transport using fluorescence microscopy. Here, in part II, we use the data from part I to develop a two-stage ordinary differential equation model of cellular electroporation. We fit our model using experimental data from cells immersed in three buffer solutions and exposed to electric field strengths of 170 to 400 kV/m and pulse durations of 1 to 1000 μs. We report that a low-conductivity 4-(2-hydroxyethyl)-1 piperazineethanesulfonic acid buffer enables molecular transport into the cell to increase more rapidly than with phosphate-buffered saline or culture medium-based buffer. For multipulse schemes, our model suggests that the interpulse delay between two opposite polarity electric field pulses does not play an appreciable role in the resultant molecular uptake for delays up to 100 μs. Our model also predicts the per-pulse permeability enhancement decreases as a function of the pulse number. This is the first report of an ordinary differential equation model of electroporation to be validated with quantitative molecular uptake data and consider both membrane permeability and charging.

Synergistic combinations of short high-voltage pulses and long low-voltage pulses enhance irreversible electroporation efficacy

Irreversible electroporation (IRE) uses ~100 μs pulsed electric fields to disrupt cell membranes for solid tumor ablation. Although IRE has achieved exciting preliminary clinical results, implementing IRE could be challenging because of volumetric limitations at the ablation region. Combining short high-voltage (SHV: 1600V, 2 μs, 1 Hz, 20 pulses) pulses with long low-voltage (LLV: 240-480 V, 100 μs, 1 Hz, 60-80 pulses) pulses induces a synergistic effect that enhances IRE efficacy. Here, cell cytotoxicity and tissue ablation were investigated. The results show that combining SHV pulses with LLV pulses induced SKOV3 cell death more effectively, and compared to either SHV pulses or LLV pulses applied alone, the combination significantly enhanced the ablation region. Particularly, prolonging the lag time (100 s) between SHV and LLV pulses further reduced cell viability and enhanced the ablation area. However, the sequence of SHV and LLV pulses was important, and the LLV + SHV combination was not as effective as the SHV + LLV combination. We offer a hypothesis to explain the synergistic effect behind enhanced cell cytotoxicity and enlarged ablation area. This work shows that combining SHV pulses with LLV pulses could be used as a focal therapy and merits investigation in larger pre-clinical models and microscopic mechanisms.

Effect of calcium electroporation in combination with metformin in vivo and correlation between viability and intracellular ATP level after calcium electroporation in vitro

Background

Calcium electroporation is a new experimental anti-cancer treatment where calcium is internalized into cells by application of short, high voltage pulses. Calcium electroporation has been shown to induce tumor necrosis associated with ATP depletion while the effect on normal fibroblasts was limited when investigated in a 3D in vitro spheroid model. We aimed to investigate the effect of calcium electroporation in combination with metformin, a drug that affects intracellular ATP level. We also aimed to study the relationship between the viability and intracellular ATP levels after calcium electroporation in vitro.

Methods

In this study, we investigated the effect of calcium electroporation with metformin on NMRI-Foxn1^nu mice in vivo on tumor size, survival, and intracellular ATP. We further investigated viability and intracellular ATP level in vitro after calcium electroporation in two human cancer cell lines: Breast (MDA-MB231) and colon (HT29), and in normal human fibroblasts (HDF-n), as well as investigating viability in human bladder cancer cells (SW780) and human small cell lung cancer cells (H69) where we have previously published intracellular ATP levels.

Results

Calcium electroporation significantly reduced the size and ATP level of bladder cancer tumors treated in vivo but no increased effect of metformin combined with calcium electroporation was shown on neither tumor size, survival, nor ATP level. Calcium electroporation in vitro significantly decreased viability compared with calcium alone (p<0.0001 for calcium concentrations from 0.5 mM for H69, HDF-n, and MDA-MB231; p<0.0001 for calcium concentrations from 1 mM for HT29 and SW780). Intracellular ATP levels decreased significantly after calcium electroporation (p<0.05), however no correlation between intracellular ATP level and viability after treatment was observed.

Conclusion

Calcium electroporation caused reduced tumor size, increased survival, and acute ATP depletion in vivo. This effect was not augmented by metformin. Calcium electroporation is a possible novel anti-cancer treatment that has been shown to cause cell death associated with acute ATP depletion in vitro and in vivo.

Multiparametric prostate magnetic resonance imaging in the evaluation of prostate cancer

Imaging has traditionally played a minor role in the diagnosis and staging of prostate cancer. However, recent controversies generated by the use of prostate-specific antigen (PSA) screening followed by random biopsy have encouraged the development of new imaging methods for prostate cancer. Multiparametric magnetic resonance imaging (mpMRI) has emerged as the imaging method best able to detect clinically significant prostate cancers and to guide biopsies. Here, the authors explain what mpMRI is and how it is used clinically, especially with regard to high-risk populations, and we discuss the impact of mpMRI on treatment decisions for men with prostate cancer. CA Cancer J Clin 2016;66:326-336. © 2015 American Cancer Society.

Irreversible electroporation: state of the art

The field of focal ablative therapy for the treatment of cancer is characterized by abundance of thermal ablative techniques that provide a minimally invasive treatment option in selected tumors. However, the unselective destruction inflicted by thermal ablation modalities can result in damage to vital structures in the vicinity of the tumor. Furthermore, the efficacy of thermal ablation intensity can be impaired due to thermal sink caused by large blood vessels in the proximity of the tumor. Irreversible electroporation (IRE) is a novel ablation modality based on the principle of electroporation or electropermeabilization, in which electric pulses are used to create nanoscale defects in the cell membrane. In theory, IRE has the potential of overcoming the aforementioned limitations of thermal ablation techniques. This review provides a description of the principle of IRE, combined with an overview of in vivo research performed to date in the liver, pancreas, kidney, and prostate.

Irreversible Electroporation (IRE): Standardization of Terminology and Reporting Criteria for Analysis and Comparison

BACKGROUND

Irreversible electroporation (IRE) as newer ablation modality has been introduced and its clinical niche is under investigation. At present just one IRE system has been approved for clinical use and is currently commercially available (NanoKnife® system). In 2014, the International Working Group on Image-Guided Tumor Ablation updated the recommendation about standardization of terms and reporting criteria for image-guided tumor ablation. The IRE method is not covered in detail. But the non-thermal IRE method and the NanoKnife System differ fundamentally from established ablations techniques, especially thermal approaches, e.g. radio frequency ablation (RFA).

MATERIAL/METHODS

As numerous publications on IRE with varying terminology exist so far - with numbers continuously increasing - standardized terms and reporting criteria of IRE are needed urgently. The use of standardized terminology may then allow for a better inter-study comparison of the methodology applied as well as results achieved.

RESULTS

Thus, the main objective of this document is to supplement the updated recommendation for image-guided tumor ablation by outlining a standardized set of terminology for the IRE procedure with the NanoKnife Sytem as well as address essential clinical and technical informations that should be provided when reporting on IRE tumor ablation.

CONCLUSIONS

We emphasize that the usage of all above recommended reporting criteria and terms can make IRE ablation reports comparable and provide treatment transparency to assess the current value of IRE and provide further development.

The Influence of a Metal Stent on the Distribution of Thermal Energy during Irreversible Electroporation

PURPOSE

Irreversible electroporation (IRE) uses short duration, high-voltage electrical pulses to induce cell death via nanoscale defects resulting from altered transmembrane potential. The technique is gaining interest for ablations in unresectable pancreatic and hepatobiliary cancer. Metal stents are often used for palliative biliary drainage in these patients, but are currently seen as an absolute contraindication for IRE due to the perceived risk of direct heating of the metal and its surroundings. This study investigates the thermal and tissue viability changes due to a metal stent during IRE.

METHODS

IRE was performed in a homogeneous tissue model (polyacrylamide gel), without and with a metal stent placed perpendicular and parallel to the electrodes, delivering 90 and 270 pulses (15-35 A, 90 μsec, 1.5 cm active tip exposure, 1.5 cm interelectrode distance, 1000-1500 V/cm, 90 pulses/min), and in-vivo in a porcine liver (4 ablations). Temperature changes were measured with an infrared thermal camera and with fiber-optic probes. Tissue viability after in-vivo IRE was investigated macroscopically using 5-triphenyltetrazolium chloride (TTC) vitality staining.

RESULTS

In the gel, direct stent-heating was not observed. Contrarily, the presence of a stent between the electrodes caused a higher increase in median temperature near the electrodes (23.2 vs 13.3°C [90 pulses]; p = 0.021, and 33.1 vs 24.8°C [270 pulses]; p = 0.242). In-vivo, no temperature difference was observed for ablations with and without a stent. Tissue examination showed white coagulation 1mm around the electrodes only. A rim of vital tissue remained around the stent, whereas ablation without stent resulted in complete tissue avitality.

CONCLUSION

IRE in the vicinity of a metal stent does not cause notable direct heating of the metal, but results in higher temperatures around the electrodes and remnant viable tissue. Future studies should determine for which clinical indications IRE in the presence of metal stents is safe and effective.

A prospective Phase 2a pilot study investigating focal percutaneous irreversible electroporation (IRE) ablation by NanoKnife in patients with localised renal cell carcinoma (RCC) with delayed interval tumour resection (IRENE trial)

INTRODUCTION

Focal ablation therapy is playing an increasing role in oncology and may reduce the toxicity of current surgical treatments while achieving adequate oncological benefit. Irreversible electroporation (IRE) has been proposed to be tissue-selective with potential advantages compared with current thermal-ablation technologies or radiotherapy. The aim of this pilot trial is to determine the effectiveness and feasibility of focal percutaneous IRE in patients with localised renal cell cancer as a uro-oncological tumour model.

METHODS

Prospective, monocentric Phase 2a pilot study following current recommendations, including those of the International Working Group on Image-Guided Tumor Ablation. Twenty patients with kidney tumour (T1aN0M0) will be recruited. This sample permits an appropriate evaluation of the feasibility and effectiveness of image-guided percutaneous IRE ablation of locally confined kidney tumours as well as functional outcomes. Percutaneous biopsy for histopathology will be performed before IRE, with magnetic-resonance imaging one day before and 2, 7, 27 and 112 days after IRE; at 28 days after IRE the tumour region will be completely resected and analysed by ultra-thin-layer histology.

DISCUSSION

The IRENE study will investigate over a short-term observation period (by magnetic-resonance imaging, post-resection histology and assessment of technical feasibility) whether focal IRE, as a new ablation procedure for soft tissue, is feasible as a percutaneous, tissue-sparing method for complete ablation and cure of localised kidney tumours. Results from the kidney-tumour model can provide guidance for designing an effectiveness and feasibility trial to assess this new ablative technology, particularly in uro-oncology.