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

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

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

SIGNIFICANCE

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

The Influence of Irreversible Electroporation Parameters on the Size of the Ablation Zone and Thermal Effects: A Systematic Review

Introduction: The aim of this study was to review the effect of irreversible electroporation parameter settings on the size of the ablation zone and the occurrence of thermal effects. This insight would help to optimize treatment protocols and effectively ablate a tumor while controlling the occurrence of thermal effects. Methods: Various individual studies report the influence of variation in electroporation parameters on the ablation zone size or occurrence of thermal effects. However, no connections have yet been established between these studies. With the aim of closing the gap in the understanding of and personalizing irreversible electroporation parameter settings, a systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A quality assessment was performed using an in-house developed grading tool based on components of commonly used grading domains. Data on the electroporation parameters voltage, number of electrodes, inter-electrode distance, active needle length, pulse length/number/protocol/frequency, and pulse interval were extracted. Ablation zone size and temperature data were grouped per parameter. Spearman correlation and linear regression were used to define the correlation with outcome measures. Results: A total of 7661 articles were screened, of which 18 preclinical studies (animal and phantom studies) met the inclusion criteria. These studies were graded as moderate (4/18) and low (14/18) quality. Only the applied voltage appeared to be a significant linear predictor of ablation zone size: length, surface, and volume. The pulse number was moderately but nonlinearly correlated with the ablation zone length. Thermal effects were more likely to occur for higher voltages (≥2000 V), higher number of electrodes, and increased active needle length. Conclusion: Firm conclusions are limited since studies that investigated and precisely reported the influence of electroporation parameters on the ablation zone size and thermal effects were scarce and mostly graded low quality. High-quality studies are needed to improve the predictability of the combined effect of variation in parameter combinations and optimize irreversible electroporation treatment protocols.

Novel irreversible electroporation ablation (Nano-knife) versus radiofrequency ablation for the treatment of solid liver tumors: a comparative, randomized, multicenter clinical study

Irreversible electroporation (IRE) is a soft tissue ablation technique that uses short electrical fields which induce the death of target cells. To evaluate the safety and efficacy of an IRE-based device compared to regular radiofrequency ablation (RFA) of solid liver tumors, in this multicenter, randomized, parallel-arm, non-inferiority study, 152 patients with malignant liver tumors were randomized into IRE (n = 78) and RFA (n = 74) groups. The primary endpoint was the success rate of tumor ablation; the secondary endpoints included the tumor ablation time, complications, tumor recurrence rates and treatment-related adverse events (TRAE). The success rate of tumor ablation using IRE was 94.9% and was non-inferior to the RFA group (96.0%) (P = 0.761). For the secondary endpoints, the average ablation time was 34.29 ± 30.38 min for the IRE group, which was significantly longer than for the RFA group (19.91 ± 16.08 min) (P < 0.001). The incidences of postoperative complications after 1 week (P = 1.000), 1 month (P = 0.610) and 3 months (P = 0.490) were not significantly different between the 2 groups. The recurrence rates of liver tumor at 1, 3 and 6 months after ablation were 0 (0.0%), 10 (13.9%) and 10 (13.3%) in the IRE group and 2.9%, 7.3% and 19.7% in the RFA control group (all P > 0.05), respectively. For safety assessments, 51 patients experienced 191 AEs (65.4%) in the IRE group, which was not different from the RFA group (73.0%, 54/184) (P = 0.646). In 7 IRE patients, 8 TRAEs (7.9%) occurred, the most common being edema of the limbs (mild grade) and fever (severe grade), while no TRAEs occurred in the RFA group. This study proved that the excellent safety and efficacy of IRE was non-inferior to the regular radiofrequency device in ablation performance for the treatment of solid liver tumors. Clinical trial registration: Chinese Clinical Trial Registry: ChiCTR1800017516

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

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

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.

Electroporation and Electrochemotherapy in Gynecological and Breast Cancer Treatment

Gynecological carcinomas affect an increasing number of women and are associated with poor prognosis. The gold standard treatment plan is mainly based on surgical resection and subsequent chemotherapy with cisplatin, 5-fluorouracil, anthracyclines, or taxanes. Unfortunately, this treatment is becoming less effective and is associated with many side effects that negatively affect patients’ physical and mental well-being. Electroporation based on tumor exposure to electric pulses enables reduction in cytotoxic drugs dose while increasing their effectiveness. EP-based treatment methods have received more and more interest in recent years and are the subject of a large number of scientific studies. Some of them show promising therapeutic potential without using any cytotoxic drugs or molecules already present in the human body (e.g., calcium electroporation). This literature review aims to present the fundamental mechanisms responsible for the course of EP-based therapies and the current state of knowledge in the field of their application in the treatment of gynecological neoplasms.

Ultralong-Time Recovery and Low-Voltage Electroporation for Biological Cell Monitoring Enabled by a Microsized Multipulse Framework

Long-term nondestructive monitoring of cells is of significant importance for understanding cell proliferation, cell signaling, cell death, and other processes. However, traditional monitoring methods are limited to a certain range of testing conditions and may reduce cell viability. Here, we present a microgap, multishot electroporation (M2E) system for monitoring cell recovery for up to ∼2 h using ∼5 V pulses and with excellent cell viability using a medium cell population. Electric field simulations reveal the bias-voltage- and gap-size-dependent electric field intensities in the M2E system. In addition to excellent transparency with low cell toxicity, the M2E system does not require specialized components, expensive materials, complicated fabrication processes, or cell manipulations; it just consists of a micrometer-sized pattern and a low-voltage square-wave generator. Ultimately, the M2E system can offer a long-term and nontoxic method of cell monitoring.

Nanosecond pulses targeting intracellular ablation increase destruction of tumor cells with irregular morphology

The decrease in killing sensitivity of the cell membrane to microsecond pulse electric fields (μs-PEFs) is ascribed mainly to the aberrant morphology of cancer cells, with clear statistical correlations observed between cell size and shape defects and the worsening of the electrical response to the PEF. In this paper, nanosecond pulsed electric fields (ns-PEFs) inducing the nucleus effect and μs-PEFs targeting the cell membrane were combined to enhance destruction of irregular cells. The fluorescence dissipation levels of the nuclear membrane and cell membrane exposed to the μs, ns, and ns + μs pulse protocols were measured and compared, and a dynamic electroporation model of irregular cells was established by the finite element software COMSOL. The results suggest that the cell membrane disruption induced by μs-PEFs is worse for extremely irregular cells and depends strongly on cellular morphology. However, the nuclear membrane disruption induced by ns-PEFs does not scale with irregularity, suggesting the use of a combination of ns-PEFs with μs-PEFs to target the nuclear and cell membranes. We demonstrate that ns + μs pulses can significantly enhance the fluorescence dissipation of the cell and nuclear membranes. Overall, our findings indicate that ns + μs pulses may be useful in the effective killing of irregular cells.

Molecular harvesting with electroporation for tissue profiling

Recent developments in personalized medicine are based on molecular measurement steps that guide personally adjusted medical decisions. A central approach to molecular profiling consists of measuring DNA, RNA, and/or proteins in tissue samples, most notably in and around tumors. This measurement yields molecular biomarkers that are potentially predictive of response and of tumor type. Current methods in cancer therapy mostly use tissue biopsy as the starting point of molecular profiling. Tissue biopsies involve a physical resection of a small tissue sample, leading to localized tissue injury, bleeding, inflammation and stress, as well as to an increased risk of metastasis. Here we developed a technology for harvesting biomolecules from tissues using electroporation. We show that tissue electroporation, achieved using a combination of high-voltage short pulses, 50 pulses 500 V cm-1, 30 µs, 1 Hz, with low-voltage long pulses 50 pulses 50 V cm-1, 10 ms, delivered at 1 Hz, allows for tissue-specific extraction of RNA and proteins. We specifically tested RNA and protein extraction from excised kidney and liver samples and from excised HepG2 tumors in mice. Further in vivo development of extraction methods based on electroporation can drive novel approaches to the molecular profiling of tumors and of tumor environment and to related diagnosis practices.

A Conceivable Mechanism Responsible for the Synergy of High and Low Voltage Irreversible Electroporation Pulses

Irreversible electroporation (IRE), is a new non-thermal tissue ablation technology in which brief high electric field pulses are delivered across the target tissue to induce cell death by irreversible permeabilization of the cell membrane. A deficiency of conventional IRE is that the ablation zone is relatively small, bounded by the irreversible electroporation isoelectric field margin. In the previous studies we have introduced a new treatment protocol that combines few short high voltage (SHV) pulses with long low-voltage (LLV) pulses. In the previous studies, we also have shown that the addition of few SHV pulses increases by almost a factor of two the area ablated by a protocol that employs only the LLV pulses. This study employs potato and gel phantom to generate a plausible explanation for the mechanism. The study provides circumstantial evidence that the mechanism involved is the production of electrolytic compounds by the LLV pulse sequence, which causes tissue ablation beyond the margin of the irreversible electroporation isoelectric field generated by the SHV pulses, presumable to the reversible electroporation isoelectric field margin generated by the SHV pulses.

Tumor Ablation Enhancement by Combining Radiofrequency Ablation and Irreversible Electroporation: An In Vitro 3D Tumor Study

We hypothesized and demonstrated for the first time that significant tumor ablation enhancement can be achieved by combining radiofrequency ablation (RFA) and irreversible electroporation (IRE) using a 3D cervical cancer cell model. Three RFA (43, 50, and 60 °C for 2 min) and IRE protocols (350, 700, and 1050 V/cm) were used to study the combining effect in the 3D tumor cell model. The in vitro experiment showed that both RFA enhanced IRE and IRE enhanced RFA can lead to a significant increase in the size of the ablation zone compared to IRE and RFA alone. It was also noted that the sequence of applying ablation energy (RFA → RE or IRE → RFA) affected the efficacy of tumor ablation enhancement. The electrical conductivity of 3D tumor was found to be increased after preliminary RFA or IRE treatment. This increase in tumor conductivity may explain the enhancement of tumor ablation. Another explanation might be that there is repeat injury to the transitional zone of the first treatment by the second one. The promising results achieved in the study can provide us useful clues about the treatment of large tumors abutting large vessels or bile ducts.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

SIGNIFICANCE

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

Development of a statistical model for cervical cancer cell death with irreversible electroporation in vitro

PURPOSE

The aim of this study was to develop a statistical model for cell death by irreversible electroporation (IRE) and to show that the statistic model is more accurate than the electric field threshold model in the literature using cervical cancer cells in vitro.

METHODS

HeLa cell line was cultured and treated with different IRE protocols in order to obtain data for modeling the statistical relationship between the cell death and pulse-setting parameters. In total, 340 in vitro experiments were performed with a commercial IRE pulse system, including a pulse generator and an electric cuvette. Trypan blue staining technique was used to evaluate cell death after 4 hours of incubation following IRE treatment. Peleg-Fermi model was used in the study to build the statistical relationship using the cell viability data obtained from the in vitro experiments. A finite element model of IRE for the electric field distribution was also built. Comparison of ablation zones between the statistical model and electric threshold model (drawn from the finite element model) was used to show the accuracy of the proposed statistical model in the description of the ablation zone and its applicability in different pulse-setting parameters.

RESULTS

The statistical models describing the relationships between HeLa cell death and pulse length and the number of pulses, respectively, were built. The values of the curve fitting parameters were obtained using the Peleg-Fermi model for the treatment of cervical cancer with IRE. The difference in the ablation zone between the statistical model and the electric threshold model was also illustrated to show the accuracy of the proposed statistical model in the representation of ablation zone in IRE.

CONCLUSIONS

This study concluded that: (1) the proposed statistical model accurately described the ablation zone of IRE with cervical cancer cells, and was more accurate compared with the electric field model; (2) the proposed statistical model was able to estimate the value of electric field threshold for the computer simulation of IRE in the treatment of cervical cancer; and (3) the proposed statistical model was able to express the change in ablation zone with the change in pulse-setting parameters.