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

Characterization of two distinct immortalized endothelial cell lines, EA.hy926 and HMEC-1, for in vitro studies: exploring the impact of calcium electroporation, Ca2+ signaling and transcriptomic profiles

BACKGROUND

Disruption of Ca2+ homeostasis after calcium electroporation (CaEP) in tumors has been shown to elicit an enhanced antitumor effect with varying impacts on healthy tissue, such as endothelium. Therefore, our study aimed to determine differences in Ca2+ kinetics and gene expression involved in the regulation of Ca2+ signaling and homeostasis, as well as effects of CaEP on cytoskeleton and adherens junctions of the established endothelial cell lines EA.hy926 and HMEC-1.

METHODS

CaEP was performed on EA.hy926 and HMEC-1 cells with increasing Ca2+ concentrations. Viability after CaEP was assessed using Presto Blue, while the effect on cytoskeleton and adherens junctions was evaluated via immunofluorescence staining (F-actin, α-tubulin, VE-cadherin). Differences in intracellular Ca2+ regulation ([Ca2+]i) were determined with spectrofluorometric measurements using Fura-2-AM, exposing cells to DPBS, ionomycin, thapsigargin, ATP, bradykinin, angiotensin II, acetylcholine, LaCl3, and GdCl3. Molecular distinctions were identified by analyzing differentially expressed genes and pathways related to the cytoskeleton and Ca2+ signaling through RNA sequencing.

RESULTS

EA.hy926 cells, at increasing Ca2+ concentrations, displayed higher CaEP susceptibility and lower survival than HMEC-1. Immunofluorescence confirmed CaEP-induced, time- and Ca2+-dependent morphological changes in EA.hy926's actin filaments, microtubules, and cell-cell junctions. Spectrofluorometric Ca2+ kinetics showed higher amplitudes in Ca2+ responses in EA.hy926 exposed to buffer, G protein coupled receptor agonists, bradykinin, and angiotensin II compared to HMEC-1. HMEC-1 exhibited significantly higher [Ca2+]i changes after ionomycin exposure, while responses to thapsigargin, ATP, and acetylcholine were similar in both cell lines. ATP without extracellular Ca2+ ions induced a significantly higher [Ca2+]i rise in EA.hy926, suggesting purinergic ionotropic P2X and metabotropic P2Y receptor activation. RNA-sequencing analysis showed significant differences in cytoskeleton- and Ca2+-related gene expression, highlighting upregulation of ORAI2, TRPC1, TRPM2, CNGA3, TRPM6, and downregulation of TRPV4 and TRPC4 in EA.hy926 versus HMEC-1. Moreover, KEGG analysis showed upregulated Ca2+ import and downregulated export genes in EA.hy926.

CONCLUSIONS

Our finding show that significant differences in CaEP response and [Ca2+]i regulation exist between EA.hy926 and HMEC-1, which may be attributed to distinct transcriptomic profiles. EA.hy926, compared to HMEC-1, displayed higher susceptibility and sensitivity to [Ca2+]i changes, which may be linked to overexpression of Ca2+-related genes and an inability to mitigate changes in [Ca2+]i. The study offers a bioinformatic basis for selecting EC models based on research objectives.

Susceptibility of various human cancer cell lines to nanosecond and microsecond range electrochemotherapy: Feasibility of multi-drug cocktails

Electrochemotherapy (ECT) involves combining anticancer drugs with electroporation, which is induced by pulsed electric fields (PEFs), while the effects vary in effectiveness based on the specific parameters of the electrical pulses and susceptibility of the cells to a specific drug. In this work, we utilized conventional microsecond electroporation protocols (0.8 - 1.5 kV/cm × 100 μs × 8, 1 Hz) and the new modality of nanosecond pulses (4 and 8 kV/cm × 500 ns × 100, 1 kHz and 1 MHz), which are compressed into a high frequency burst. Sensitive and resistant lung, breast and ovarian human cancer cell lines were used in the study. In order to overcome drug-resistance, we have investigated the feasibility to use anticancer drug cocktails i.e., bleomycin and cisplatin combinations with metformin, vinorelbine and Dp44mT. The different susceptibility of various human cancer cells lines to electric pulses was determined, the efficacy of ECT was characterized and the type of cell death depending on the combinations of drugs was investigated. The results indicate that synergistic effects of PEFs with drug cocktails may be used to overcome drug-resistance in cancer, while the application of nsPEF provides more flexibility in parametric protocols and modulation of cancer cell death.

Evaluation of the Anticancer Activity of Calcium Ions Introduced into Human Breast Adenocarcinoma Cells MCF-7/WT and MCF-7/DOX by Electroporation

Breast cancer ranks among the top three most common malignant neoplasms in Poland. The use of calcium ion-assisted electroporation is an alternative approach to the classic treatment of this disease. The studies conducted in recent years confirm the effectiveness of electroporation with calcium ions. Electroporation is a method that uses short electrical pulses to create transitional pores in the cell membrane to allow the penetration of certain drugs. The aim of this study was to investigate the antitumor effects of electroporation alone and calcium ion-assisted electroporation on human mammary adenocarcinoma cells that are sensitive (MCF-7/WT) and resistant to doxorubicin (MCF-7/DOX). The cell viability was assessed using independent tests: MTT and SRB. The type of cell death after the applied therapy was determined by TUNEL and flow cytometry (FACS) methods. The expression of Cav3.1 and Cav3.2 proteins of T-type voltage-gated calcium channels was assessed by immunocytochemistry, and changes in the morphology of CaEP-treated cells were visualized using a holotomographic microscope. The obtained results confirmed the effectiveness of the investigated therapeutic method. The results of the work constitute a good basis for planning research at the in vivo level and in the future to develop a more effective and safer method of breast cancer treatment for patients.

The effectiveness of calcium electroporation combined with gene electrotransfer of a plasmid encoding IL-12 is tumor type-dependent

Introduction

In calcium electroporation (CaEP), electroporation enables the cellular uptake of supraphysiological concentrations of Ca2+, causing the induction of cell death. The effectiveness of CaEP has already been evaluated in clinical trials; however, confirmatory preclinical studies are still needed to further elucidate its effectiveness and underlying mechanisms. Here, we tested and compared its efficiency on two different tumor models to electrochemotherapy (ECT) and in combination with gene electrotransfer (GET) of a plasmid encoding interleukin-12 (IL-12). We hypothesized that IL-12 potentiates the antitumor effect of local ablative therapies as CaEP and ECT.

Methods

The effect of CaEP was tested in vitro as well as in vivo in murine melanoma B16-F10 and murine mammary carcinoma 4T1 in comparison to ECT with bleomycin. Specifically, the treatment efficacy of CaEP with increasing calcium concentrations alone or in combination with IL-12 GET in different treatment protocols was investigated. We closely examined the tumor microenvironment by immunofluorescence staining of immune cells, as well as blood vessels and proliferating cells.

Results

In vitro, CaEP and ECT with bleomycin reduced cell viability in a dose-dependent manner. We observed no differences in sensitivity between the two cell lines. A dose-dependent response was also observed in vivo; however, the efficacy was better in 4T1 tumors than in B16-F10 tumors. In 4T1 tumors, CaEP with 250 mM Ca resulted in more than 30 days of growth delay, which was comparable to ECT with bleomycin. In contrast, adjuvant peritumoral application of IL-12 GET after CaEP prolonged the survival of B16-F10, but not 4T1-bearing mice. Moreover, CaEP with peritumoral IL-12 GET modified tumor immune cell populations and tumor vasculature.

Conclusions

Mice bearing 4T1 tumors responded better to CaEP in vivo than mice bearing B16-F10 tumors, even though a similar response was observed in vitro. Namely, one of the most important factors might be involvement of the immune system. This was confirmed by the combination of CaEP or ECT with IL-12 GET, which further enhanced antitumor effectiveness. However, the potentiation of CaEP effectiveness was also highly dependent on tumor type; it was more pronounced in poorly immunogenic B16-F10 tumors compared to moderately immunogenic 4T1 tumors.

Nanoelectropulse delivery for cell membrane perturbation and oxidation in human colon adenocarcinoma cells with drug resistance

Ultrashort electric pulses in the nanosecond range (nsPEF) can affect extra- and intracellular lipid structures and can also alternate cell functioning reversibly and irreversibly. Several of the nsPEF effects are due to the abrupt rise in intracellular free calcium levels and calcium ions influx from the outside. Calcium is one of the most important factors in cell proliferation, differentiation, and cell death (apoptosis or necrosis). Manipulating calcium levels using electroporation can have different effects on normal and malignant cells. This study aimed to examine the impact of nsPEFs, combined with 1 mM Ca²⁺ in human colon adenocarcinoma cell lines: sensitive- LoVo and drug resistant-LoVoDX. In this study 200 pulses of 10 ns and high voltage (12.5-50 kVcm^-1) were used. Cell viability was determined by MTT and clonogenic assay. Proteasomal activity, GSH/GSSG assay, ROS production, and PALS-1 protein were evaluated as oxidative stress markers and protein damage. Cell morphology was visualized by AFM, SEM, and confocal microscopy imaging. The results revealed that nsPEF with 1 mM Ca²⁺ is cytotoxic, particularly for LoVoDX cells, and safe for normal cells. NsPEF provoked ROS release, altered cell polarity, and destabilized cell morphology. These results can be important for future protocols for colon adenocarcinoma using calcium nsPEF.

Pulsed electric fields with calcium ions stimulate oxidative alternations and lipid peroxidation in human non-small cell lung cancer

Pulsed electric fields (PEFs) are commonly used to facilitate the delivery of various molecules, including pharmaceuticals, into living cells. However, the applied protocols still require optimization regarding the conditions of the permeabilization process, i.e., pulse waveform, voltage, duration, and the number of pulses in a burst. This study highlights the importance of electrochemical processes involved in the electropermeabilization process, known as electroporation. This research investigated the effects of electroporation on human non-small cell lung cancer cells (A549) in potassium (SKM) and HEPES-based buffers (SHM) using sub-microsecond and microsecond range pulses. The experiments were performed using 100 ns - 100 μs (0.6-15 kV/cm) bursts with 8 pulses in a sequence. It was shown that depending on the buffer composition, the susceptibility of cells to PEF varies, while calcium enhances the cytotoxic effects of PEF, if high cell membrane permeabilization is triggered. It was also determined that electroporation with calcium ions induces oxidative stress in cells, including lipid peroxidation (LPO), generation of reactive oxygen species (ROS), and neutral lipid droplets. Here, we demonstrated that calcium ions and optimized pulse parameters could potentiate PEF efficacy and oxidative alternations in lung cancer cells. Thus, the anticancer efficacy of PEF in lung cancers in combination with standard cytostatic drugs or calcium ions should be considered, but this issue still requires in-depth detailed studies with in vivo models.

Calcium Electroporation Reduces Viability and Proliferation Capacity of Four Uveal Melanoma Cell Lines in 2D and 3D Cultures

Simple Summary

Calcium electroporation (CaEP) is an innovative anti-tumor treatment modality that induces cell death by introducing supraphysiological concentrations of calcium into cells with a limited effect on normal cells. The objective of the present study is to assess the effect of CaEP in uveal melanoma (UM) cell lines in comparison to electrochemotherapy (ECT) with bleomycin using 2D monolayer cell cultures as well as 3D tumor spheroid models in four different UM cell lines. The morphological changes of the spheroids, the cell viability, growth rate as well as the cytotoxic effect of electroporation (EP) with calcium chloride and bleomycin were evaluated with various drug concentrations. The results of CaEP and ECT both suggest a comparable dose-dependent reduction in cell viability and proliferation rate in all tested 2D cell lines and 3D tumor spheroids. These data point out that CaEP is an established anticancer treatment causing cell death by ATP depletion in in vitro and in vivo, representing an efficient alternative therapy with a lower cytotoxic potency for the local UM tumor control.

Abstract

Electrochemotherapy (ECT) is the combination of transient pore formation following electric pulse application with the administration of cytotoxic drugs, which enhances the cytotoxic effect of the applied agent due to membrane changes and permeabilization. Although EP represents an established therapeutic option for solid malignancies, recent advances shift to the investigation of non-cytotoxic agents, such as calcium, which can also induce cell death. The present study aims to evaluate the cytotoxic effect, the morphological changes in tumor spheroids, the effect on the cell viability, and the cell-specific growth rate following calcium electroporation (CaEP) in uveal melanoma (UM) 2D monolayer cell cultures as well as in 3D tumor spheroid models. The experiments were conducted in four cell lines, UM92.1, Mel270, and two primary UM cell lines, UPMD2 and UPMM3 (UPM). The 2D and 3D UM cell cultures were electroporated with eight rectangular pulses (100 µs pulse duration, 5 Hz repetition frequency) of a 1000 V/cm pulse strength alone or in combination with 0.11 mg/mL, 0.28 mg/mL, 0.55 mg/mL or 1.11 mg/mL calcium chloride or 1.0 µg/mL or 2.5 µg/mL bleomycin. The application of calcium chloride alone induced an ATP reduction only in the UM92.1 2D cell cultures. Calcium alone had no significant effect on ATP levels in all four UM spheroids. A significant decrease in the intracellular adenosine triphosphate (ATP) level was documented in all four 2D and 3D cell cultures for both CaEP as well as ECT with bleomycin. The results suggest a dose-dependent ATP depletion with a wide range of sensitivity among the tested UM cell lines, control groups, and the applied settings in both 2D monolayer cell cultures and 3D tumor spheroid models. The colony formation capacity of the cell lines after two weeks reduced significantly after CaEP only with 0.5 mg/mL and 1.1 mg/mL, whereas the same effect could be achieved with both applied bleomycin concentrations, 1.0 µg/mL and 2.5 µg/mL, for the ECT group. The specific growth rate on day 7 following CaEP was significantly reduced in UM92.1 cell lines with 0.5 and 1.1 mg/mL calcium chloride, while Mel270 showed a similar effect only after administration of 1.1 mg/mL. UM92.1 and Mel270 spheroids exhibited lower adhesion and density after CaEP on day three in comparison to UPM spheroids showing detachment after day 7 following treatment. CaEP and bleomycin electroporation significantly reduce cell viability at similar applied voltage settings. CaEP may be a feasible and inexpensive therapeutic option for the local tumor control with fewer side effects, in comparison to other chemotherapeutic agents, for the treatment of uveal melanoma. The limited effect on normal cells and the surrounding tissue has already been investigated, but further research is necessary to clarify the effect on the surrounding tissue and to facilitate its application in a clinical setting for the eye.

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.

Calcium ion effect on phospholipid bilayers as cell membrane analogues

Ion attachment can modify stability and structure of phospholipid bilayers. Of particular importance is the interaction of phospholipids with divalent cations, such as calcium ions playing an important role in numerous cellular processes. The aim of our study was to determine effects of calcium ions on phospholipid membranes employing two cell membrane analogues, liposomes and planar lipid bilayers, and for the first time the combination of two instrumental setups: gas-phase electrophoresis (nES GEMMA instrumentation) and electrical (capacitance and resistance) measurements. Liposomes and planar lipid bilayers consisted of phosphatidylcholine, cholesterol and phosphatidylethanolamine. Liposomes were prepared from dried lipid films via hydration while planar lipid bilayers were formed using a Mueller-Rudin method. Calcium ions were added to membranes from higher concentrated stock solutions. Changes in phospholipid bilayer properties due to calcium presence were observed for both studied cell membrane analogues. Changes in liposome size were observed, which might either be related to tighter packing of phospholipids in the bilayer or local distortions of the membrane. Likewise, a measurable change in planar lipid bilayer resistance and capacitance was observed in the presence of calcium ions, which can be due to an increased rigidity and tighter packing of the lipid molecules in the bilayer.

New therapeutic strategy: Personalization of pancreatic cancer treatment-irreversible electroporation (IRE), electrochemotherapy (ECT) and calcium electroporation (CaEP) - A pilot preclinical study

In this study, irreversible electroporation (IRE), electrochemotherapy (ECT), and calcium electroporation (CaEP) techniques were investigated as new strategies for human pancreatic cancer. Qualification of the patients, best "therapeutic moment" for each patient, safety, and complications after procedures were examined. In this pilot study were included 13 patients in this study, which were operated on in different pancreatic cancer stages. Patients underwent IRE or ECT with intravenous admission of cisplatin or electroporation with calcium intratumoral administration. The IRE procedure was safe for the patients. Medium overall survival for IRE, IRE + CTH, and IRE + CaCl₂ was respectively: 16, 29.5, and 19 months comparing to 10 months in control chemotherapy (CTH) group. Thus, IRE, ECT, and CaEP can be effective strategies for pancreatic cancer treatment.

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.

Electroporation-Based Treatments in Urology

The observation that an application of a pulsed electric field (PEF) resulted in an increased permeability of the cell membrane has led to the discovery of the phenomenon called electroporation (EP). Depending on the parameters of the electric current and cell features, electroporation can be either reversible or irreversible. The irreversible electroporation (IRE) found its use in urology as a non-thermal ablative method of prostate and renal cancer. As its mechanism is based on the permeabilization of cell membrane phospholipids, IRE (as well as other treatments based on EP) provides selectivity sparing extracellular proteins and matrix. Reversible EP enables the transfer of genes, drugs, and small exogenous proteins. In clinical practice, reversible EP can locally increase the uptake of cytotoxic drugs such as cisplatin and bleomycin. This approach is known as electrochemotherapy (ECT). Few in vivo and in vitro trials of ECT have been performed on urological cancers. EP provides the possibility of transmission of genes across the cell membrane. As the protocols of gene electrotransfer (GET) over the last few years have improved, EP has become a well-known technique for non-viral cell transfection. GET involves DNA transfection directly to the cancer or the host skin and muscle tissue. Among urological cancers, the GET of several plasmids encoding prostate cancer antigens has been investigated in clinical trials. This review brings into discussion the underlying mechanism of EP and an overview of the latest progress and development perspectives of EP-based treatments in urology.

Effects of extracellular medium conductivity on cell response in the context of sub-microsecond range calcium electroporation

In the present study, we report the effects of extracellular medium conductivity on cell response in the context of sub-microsecond range (100 ns-900 ns) electroporation, calcium electroporation and cell size. The effects of 25 ns and microsecond range (100 μs) pulses were also covered. As a model, three different cancer cell lines of various size (C32, MCF-7/DX and MC38/0) were used and the results indicated different size-dependent susceptibility patterns to the treatment. The applied pulsed electric field (PEF) protocols revealed a significant decrease of cell viability when calcium electroporation was used. The dependence of calcium ion transport and finally the anticancer effect on the external medium conductivity was determined. It was shown that small differences in conductivity do not alter viability significantly, however, mostly affect the permeabilization. At the same, MC38/0 cell line was the least susceptible to calcium electroporation, while the C32 line the most. In all cases calcium electroporation was mostly dependent on the sensitivity of cells to electroporation and could not be effectively improved by the increase of CaCl₂ concentration from 2 mM to 5 mM. Lastly, sub-microsecond PEF stimulated aquaporin-4 and VDAC1/Porin immunoreactions in all treated cells lines, which indicated that cell water balance is affected, ions exchange is increased and release of mitochondrial products is occurrent.

Chemical Enhancement of Irreversible Electroporation: A Review and Future Suggestions

Irreversible electroporation has raised great interest in the past decade as a means of destroying cancers in a way that does not involve heat. Irreversible electroporation is a novel ablation technology that uses short high-voltage electrical pulses to enhance the permeability of tumor cell membranes and generate irreversible nano-sized structural defects or pores, thus leading to cell death. Irreversible electroporation has many advantages over thermal therapies due to its nonthermal mechanism: (1) reduced risk of injury to surrounding organs and (2) no “heat-sink” effect due to nearby blood vessels. However, so far, it has been difficult for irreversible electroporation to completely ablate large tumors (eg, >3 cm in diameter). In order to overcome this problem, many preclinical and clinical studies have been performed to improve the efficacy of IRE in the treatment of large size of tumors through a chemical perspective. Due to the distribution of electric field, irreversible electroporation region, reversible electroporation region, and intact region can be found in the treatment of irreversible electroporation. Thus, 2 types of chemical enhancements of irreversible electroporation were discussed in the article, such as the reversible electroporation region enhanced and the irreversible electroporation region enhanced. Specifically, the state-of-the-art results regarding the following approaches that have the potential to be used in the enhancement of irreversible electroporation were systematically reviewed in the article, including (1) combination with cytotoxic drugs, (2) calcium electroporation, (3) modification of cell membrane, and (4) modification of the tumor cell microenvironment. In the end, we concluded with 4 issues that should be addressed in the future for improving irreversible electroporation further in a chemical way.

Calcium Delivery by Electroporation Induces In Vitro Cell Death through Mitochondrial Dysfunction without DNA Damages

Adolescent cancer survivors present increased risks of developing secondary malignancies due to cancer therapy. Electrochemotherapy is a promising anti-cancer approach that potentiates the cytotoxic effect of drugs by application of external electric field pulses. Clinicians proposed to associate electroporation and calcium. The current study aims to unravel the toxic mechanisms of calcium electroporation, in particular if calcium presents a genotoxic profile and if its cytotoxicity comes from the ion itself or from osmotic stress. Human dermal fibroblasts and colorectal HCT-116 cell line were treated by electrochemotherapy using bleomycin, cisplatin, calcium, or magnesium. Genotoxicity, cytotoxicity, mitochondrial membrane potential, ATP content, and caspases activities were assessed in cells grown on monolayers and tumor growth was assayed in tumor spheroids. Results in monolayers show that unlike cisplatin and bleomycin, calcium electroporation induces cell death without genotoxicity induction. Its cytotoxicity correlates with a dramatic fall in mitochondrial membrane potential and ATP depletion. Opposite of magnesium, over seven days of calcium electroporation led to spheroid tumor growth regression. As non-genotoxic, calcium has a better safety profile than conventional anticancer drugs. Calcium is already authorized by different health authorities worldwide. Therefore, calcium electroporation should be a cancer treatment of choice due to the reduced potential of secondary malignancies.

A Comprehensive Review of Calcium Electroporation -A Novel Cancer Treatment Modality

Calcium electroporation is a potential novel anti-cancer treatment where high calcium concentrations are introduced into cells by electroporation, a method where short, high voltage pulses induce transient permeabilisation of the plasma membrane allowing passage of molecules into the cytosol. Calcium is a tightly regulated, ubiquitous second messenger involved in many cellular processes including cell death. Electroporation increases calcium uptake leading to acute and severe ATP depletion associated with cancer cell death. This comprehensive review describes published data about calcium electroporation applied in vitro, in vivo, and clinically from the first publication in 2012. Calcium electroporation has been shown to be a safe and efficient anti-cancer treatment in clinical studies with cutaneous metastases and recurrent head and neck cancer. Normal cells have been shown to be less affected by calcium electroporation than cancer cells and this difference might be partly induced by differences in membrane repair, expression of calcium transporters, and cellular structural changes. Interestingly, both clinical data and preclinical studies have indicated a systemic immune response induced by calcium electroporation. New cancer treatments are needed, and calcium electroporation represents an inexpensive and efficient treatment with few side effects, that could potentially be used worldwide and for different tumor types.

Evaluation of Calcium Electroporation for the Treatment of Cutaneous Metastases: A Double Blinded Randomised Controlled Phase II Trial

Calcium electroporation (Ca-EP) is a new anticancer treatment providing similar features to electrochemotherapy (ECT). The aim of our study is to compare the efficacy of Ca-EP with bleomycin-based ECT. This double-blinded randomized controlled phase II study was conducted at the Medical University of Szeged, Hungary. During this once only treatment up to ten measurable cutaneous metastases per patient were separately block randomized for intratumoral delivery of either calcium or bleomycin, which was followed by reversible electroporation. Tumour response was evaluated clinically and histologically six months after treatment. (ClinicalTrials.gov: NCT03628417, closed). Seven patients with 44 metastases (34 from malignant melanoma, 10 from breast cancer) were included in the study. Eleven metastases were taken for biopsies, and 33 metastases were randomised and treated once. The objective response rates were 33% (6/18) for Ca-EP and 53% (8/15) for bleomycin-based ECT, with 22% (4/18) and 40% (6/15) complete response rates, respectively. The CR was confirmed histologically in both arms. Serious adverse events were not registered. Ulceration and hyperpigmentation, both CTCA criteria grade I side effects, were observed more frequently after bleomycin-based ECT than for Ca-EP. Ca-EP was non-inferior to ECT, therefore, it should be considered as a feasible, effective and safe treatment option.

Recent Advances in Electrochemotherapy

Electrochemotherapy is gaining recognition as an effective local therapy that uses systemically or intratumorally injected bleomycin or cisplatin with electroporation as a delivery system that brings drugs into the cells to exert their cytotoxic effects. Preclinical work is still ongoing, testing new drugs, seeking the best treatment combination with other treatment modalities, and exploring new sets of pulses for effective tissue electroporation. The applications of electrochemotherapy are being fully exploited in veterinary oncology, where electrochemotherapy, because of its simple execution, has a relatively good cost-benefit ratio and is used in the treatment of cutaneous tumors. In human oncology, electrochemotherapy is fully recognized as a local therapy for cutaneous tumors and metastases. Its effectiveness is being explored in combination with immunomodulatory drugs. However, the development of electrochemotherapy is directed into the treatment of deep-seated tumors with a percutaneous approach. Because of the vast number of reports, this review discusses the articles published in the past 5 years.

Antitumor Response and Immunomodulatory Effects of Sub-Microsecond Irreversible Electroporation and Its Combination with Calcium Electroporation

In this work, we have investigated the feasibility of sub-microsecond range irreversible electroporation (IRE) with and without calcium electroporation in vivo. As a model, BALB/C mice were used and bioluminescent SP2/0 myeloma tumor models were developed. Tumors were treated with two separate pulsed electric field (PEF) pulsing protocols PEF1: 12 kV/cm × 200 ns × 500 (0.006 J/pulse) and PEF2: 12 kV/cm × 500 ns × 500 (0.015 J/pulse), which were delivered with and without Ca²⁺ (168 mM) using parallel plate electrodes at a repetition frequency of 100 Hz. Both PEF1 and PEF2 treatments reduced tumor growth and prolonged the life span of the mice, however, the PEF2 protocol was more efficient. The delay in tumor renewal was the biggest when a combination of IRE with calcium electroporation was used, however, we did not obtain significant differences in the final mouse survival compared to PEF2 alone. Anti-tumor immune responses were also investigated after treatment with PEF2 and PEF2+Ca. In both cases the treated mice had enlarged spleens and increased spleen T cell numbers, lower percentages of suppressor cell subsets (conventional CD4⁺CD25⁺ Treg, CD4⁺CD25⁻DX5⁺ Tr1, CD8⁺DX5⁺, CD4⁺CD28⁻, CD8⁺CD28⁻), changed proportions of Tcm and Tef/Tem T cells in the spleen and increased amount of tumor cell specific antibodies in the sera. The treatment based on IRE was effective against primary tumors, destroyed the tumor microenvironment and induced an anti-tumor immune response, however, it was not sufficient for complete control of tumor metastasis.

Calcium electroporation and electrochemotherapy for cancer treatment: Importance of cell membrane composition investigated by lipidomics, calorimetry and in vitro efficacy

Calcium electroporation is a novel anti-cancer treatment investigated in clinical trials. We explored cell sensitivity to calcium electroporation and electroporation with bleomycin, using viability assays at different time and temperature points, as well as heat calorimetry, lipidomics, and flow cytometry. Three cell lines: HT29 (colon cancer), MDA-MB231 (breast cancer), and HDF-n (normal fibroblasts) were investigated for; (a) cell survival dependent on time of addition of drug relative to electroporation (1.2 kV/cm, 8 pulses, 99 µs, 1 Hz), at different temperatures (37 °C, 27 °C, 17 °C); (b) heat capacity profiles obtained by differential scanning calorimetry without added calcium; (c) lipid composition by mass spectrometry; (d) phosphatidylserine in the plasma membrane outer leaflet using flow cytometry. Temperature as well as time of drug administration affected treatment efficacy in HT29 and HDF-n cells, but not MDA-MB231 cells. Interestingly the HT29 cell line displayed a higher phase transition temperature (approximately 20 °C) versus 14 °C (HDF-n) and 15 °C (MDA-MB231). Furthermore the HT29 cell membranes had a higher ratio of ethers to esters, and a higher expression of phosphatidylserine in the outer leaflet. In conclusion, lipid composition and heat capacity of the membrane might influence permeabilisation of cells and thereby the effect of calcium electroporation and electrochemotherapy.

A Review on Differences in Effects on Normal and Malignant Cells and Tissues to Electroporation-Based Therapies: A Focus on Calcium Electroporation

Calcium electroporation is a potential novel anticancer treatment, where high concentrations of calcium are introduced into the cell cytosol by electroporation. This is a method where short, high-voltage pulses induce a transient permeabilization of the cell membrane and thereby allow influx and efflux of ions and molecules. Electroporation is used in combination with chemotherapeutic drugs (electrochemotherapy) as a standard treatment for cutaneous metastases, and electroporation using a higher electric field and number of pulses (irreversible electroporation) is increasingly being used as an anticancer treatment. In this review, calcium electroporation is described with emphasis on the investigations of differences in the effect on normal and malignant cells and tissues in vitro and in vivo. Calcium electroporation has been shown to induce cell death in vitro and tumor necrosis in vivo with a difference in sensitivity between different tumor types. Normal cells treated in vitro are significantly less affected than cancer cells, and a similar trend is shown in vivo where muscle and skin tissue surrounding a treated tumor as well as muscle and skin directly treated with calcium electroporation were less affected than tumors. The mechanism behind this difference in sensitivity is not fully understood but might be affected by differences in electric impedance, membrane repair, and expression of plasma membrane calcium ATPases in normal and malignant cells. The research on calcium electroporation shows a potential novel anticancer treatment with significant effect on cancer cells and tissues while normal cells and tissues are clearly less affected.

ESOPE-Equivalent Pulsing Protocols for Calcium Electroporation: An In Vitro Optimization Study on 2 Cancer Cell Models

Reversible electroporation is used to increase the uptake of chemotherapeutic drugs in local tumor treatment (electrochemotherapy) by applying the pulsing protocol (8 rectangular pulses, 1000 V/cm, 100 µs) standardized in the framework of the European Standard Operating Procedure on Electrochemotherapy multicenter trial. Currently, new electrochemotherapy strategies are under development to extend its applicability to tumors with different histology. Electrical parameters and drug type are critical factors. A possible approach is to test pulse parameters different from European Standard Operating Procedure on Electrochemotherapy but with comparable electroporation yield (European Standard Operating Procedure on Electrochemotherapy-equivalent protocols). Moreover, the use of non-toxic drugs combined with electroporation represents the new frontier for electrochemotherapy applications; calcium electroporation has been recently proposed as a simple tool for anticancer therapy. In vitro investigations facilitate the optimization of electrical parameters and drugs for in vivo and clinical testing. In this optimization study, new pulsing protocols have been tested by increasing the pulse number and reducing the electric field with respect to the standard. European Standard Operating Procedure on Electrochemotherapy-equivalent protocols have been identified in HL-60 and A431 cancer cell models, and a higher sensitivity in terms of electroporation yield has been recorded in HL-60 cells. Moreover, cell killing efficacy of European Standard Operating Procedure on Electrochemotherapy-equivalent protocols has been demonstrated in the presence of increasing calcium concentrations on both cell lines. Equivalent European Standard Operating Procedure on Electrochemotherapy protocols can be used to optimize the therapeutic effects in the clinic, where different regions of the same cancer tissue, with different electrical properties, might result in a differential electroporation yield of the standard protocol over the same tissue, or, eventually, in an override of the operational limits of the instrument. Moreover, using calcium can help overcome the drawbacks of standard drugs (side effects, high costs, difficult handling, preparation, and storage procedures). These results support the possibility of new treatment options in both standard electrochemotherapy and calcium electroporation, with clear advantages in the clinic.

Patterns of calcium signaling: A link between chronic emotions and cancer

Intra and inter-cellular calcium signaling is present in all types of cells and body tissues. In the human brain, calcium currents and waves are related to mental activities, including emotions. We present a theoretical interpretation of these phenomena suggesting their involvement in chronic emotional patterns and in the pathology of cancer. Recent developments on biophysics, translational biology and psychoneuroendocrinoimmunology (PNEI) can support explanatory hypotheses about the link between emotional stresses and the origin and development of different types of tumor cells. Chronic stresses may cause perturbations of rhythms of the PNEI system, excessive activation of HPA axis and abnormal activation of calcium signals in somatic tissues, with deleterious effects on different parts of the body. The increasing of calcium signaling inside cells may lead to a deregulation of different pathways and epigenetic systems that promote the production of genomic mutations in a second phase. In particular, the hyperactivation of the transcription nuclear factor kappaB (NF-κB), if is not counterbalanced by the following activation of the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or Nrf2), increases the production of oxidative catabolites, as the advanced glycation end products (AGE), which play a key role in the progression of different types of cancer and other degenerative diseases. Cortisol binding to glucocorticoid receptor (GR) reduces the activity of both NF-κB and Nrf2 inside the cells but inhibits the cellular immunity and the anabolic processes of tissue regeneration. The tissue atrophy and the defective anti-ageing mechanisms promotes the tumoral cells growth and their escape from the immune-surveillance.

Effect of calcium electroporation on tumour vasculature

Calcium electroporation (CaEP) is a novel anti-tumour treatment that induces cell death by internalization of large quantities of calcium. The anti-tumour effectiveness of CaEP has been demonstrated in vitro, in vivo, and in preliminary clinical trials; however, its effects on the vasculature have not been previously investigated. Using a dorsal window chamber tumour model, we observed that CaEP affected to the same degree normal and tumour blood vessels in vivo, as it disrupted the vessels and caused tumour eradication by necrosis. In all cases, the effect was more pronounced in small vessels, similar to electrochemotherapy (ECT) with bleomycin. In vitro studies in four different cell lines (the B16F1 melanoma, HUVEC endothelial, FADU squamous cell carcinoma, and CHO cell lines) confirmed that CaEP causes necrosis associated with acute and severe ATP depletion, a picture different from bleomycin with electroporation. Furthermore, CaEP considerably inhibited cell migratory capabilities of endothelial cells and their potential to form capillary-like structures. The finding that CaEP has anti-vascular effects and inhibits cell migration capabilities may contribute to the explanation of the high efficacy observed in preclinical and clinical studies.

Calcium electroporation for treatment of sarcoma in preclinical studies

Calcium electroporation (CaEP) describes the use of electric pulses (electroporation) to transiently permeabilize cells to allow supraphysiological doses of calcium to enter the cytosol. Calcium electroporation has successfully been investigated for treatment of cutaneous metastases in a clinical study. This preclinical study explores the possible use of calcium electroporation for treatment of sarcoma.

A normal murine muscle cell line (C2C12), and a human rhabdomyosarcoma cell line (RD) were used in the undifferentiated and differentiated state. Electroporation was performed using 8 pulses of 100 μs at 600–1000 V/cm; with calcium (0, 0.5, 1, and 5 mM). Viability was examined by MTS assay, intracellular calcium levels were measured, and expression of plasma membrane calcium ATPase (PMCA) was investigated using western blotting. Calcium/sodium exchanger (NCX1), ryanodine receptor (RyR1) expression and cytoskeleton structure (zyxin/actin) were assessed by immunofluorescence. CaEP efficiency on RD tumors was tested in vivo in immuno-deficient mice.

CaEP was significantly more efficient in RD than in normal cells. Intracellular Ca²⁺ levels after CaEP increased significantly in RD, whereas a lower increase was seen in normal cells. CaEP caused decreased expression of PMCA and NCX1 in malignant cells and RyR1 in both cell lines whereas normal cells exhibited increased expression of NCX1 after CaEP. Calcium electroporation also affected cytoskeleton structure in malignant cells.

This study showed that calcium electroporation is tolerated significantly better in normal muscle cells than sarcoma cells and as an inexpensive and simple cancer treatment this could potentially be used in connection with sarcoma surgery for local treatment.

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.