Electrochemotherapy – An easy, highly effective and safe treatment of cutaneous and subcutaneous metastases: Results of ESOPE (European Standard Operating Procedures of Electrochemotherapy) study

The influence of skeletal muscle anisotropy on electroporation: in vivo study and numerical modeling

The aim of this study was to theoretically and experimentally investigate electroporation of mouse tibialis cranialis and to determine the reversible electroporation threshold values needed for parallel and perpendicular orientation of the applied electric field with respect to the muscle fibers. Our study was based on local electric field calculated with three-dimensional realistic numerical models, that we built, and in vivo visualization of electroporated muscle tissue. We established that electroporation of muscle cells in tissue depends on the orientation of the applied electric field; the local electric field threshold values were determined (pulse parameters: 8 × 100 μs, 1 Hz) to be 80 V/cm and 200 V/cm for parallel and perpendicular orientation, respectively. Our results could be useful electric field parameters in the control of skeletal muscle electroporation, which can be used in treatment planning of electroporation based therapies such as gene therapy, genetic vaccination, and electrochemotherapy.

Preclinical analysis of irreversible electroporation on rat liver tissues using a microfabricated electroporator

A microfabricated electroporator (MFE) for the irreversible electroporation (IRE) of tissues has been developed by miniaturizing a clinical electroporator with a two-needle array while keeping the same electric field strength distribution. Since IRE was brought to special attention as one of the local tissue ablation techniques to treat tumors, many preclinical studies have been conducted to investigate the efficacy of IRE on animal tissues. However, some technical difficulties have been frequently encountered due to the macroscale dimension of clinical electroporators, particularly in experiments on small animal models such as the mouse or rat. Here, the MFE was proposed to solve the associated problems, resulting in time- and cost-effective experimental procedures. With the developed MFE, the effect of IRE on rat liver tissues was analyzed with time by immunohistological stainings and electrical measurement, and the experimental results were compared with those operated with the corresponding real-scale clinical electroporator.

Electro-mediated gene transfer and expression are controlled by the life-time of DNA/membrane complex formation

BACKGROUND

Electroporation is a physical method used to transfer molecules into cells and tissues. Clinical applications have been developed for antitumor drug delivery. Clinical trials of gene electrotransfer are under investigation. However, knowledge about how DNA enters cells is not complete. By contrast to small molecules that have direct access to the cytoplasm, DNA forms a long lived complex with the plasma membrane and is transferred into the cytoplasm with a considerable delay.

METHODS

To increase our understanding of the key step of DNA/membrane complex formation, we investigated the dependence of DNA/membrane interaction and gene expression on electric pulse polarity and repetition frequency.

RESULTS

We observed that both are affected by reversing the polarity and by increasing the repetition frequency of pulses. The results obtained in the present study reveal the existence of two classes of DNA/membrane interaction: (i) a metastable DNA/membrane complex from which DNA can leave and return to external medium and (ii) a stable DNA/membrane complex, where DNA cannot be removed, even by applying electric pulses of reversed polarity. Only DNA belonging to the second class leads to effective gene expression.

CONCLUSIONS

The life-time of DNA/membrane complex formation is of the order of 1 s and has to be taken into account to improve protocols of electro-mediated gene delivery.

Towards treatment planning and treatment of deep-seated solid tumors by electrochemotherapy

Background

Electrochemotherapy treats tumors by combining specific chemotherapeutic drugs with an intracellular target and electric pulses, which increases drug uptake into the tumor cells. Electrochemotherapy has been successfully used for treatment of easily accessible superficial tumor nodules. In this paper, we present the first case of deep-seated tumor electrochemotherapy based on numerical treatment planning.

Methods

The aim of our study was to treat a melanoma metastasis in the thigh of a patient. Treatment planning for electrode positioning and electrical pulse parameters was performed for two different electrode configurations: one with four and another with five long needle electrodes. During the procedure, the four electrode treatment plan was adopted and the patient was treated accordingly by electrochemotherapy with bleomycin. The response to treatment was clinically and radiographically evaluated. Due to a partial response of the treated tumor, the metastasis was surgically removed after 2 months and pathological analysis was performed.

Results

A partial response of the tumor to electrochemotherapy was obtained. Histologically, the metastasis showed partial necrosis due to electrochemotherapy, estimated to represent 40-50% of the tumor. Based on the data obtained, we re-evaluated the electrical treatment parameters in order to correlate the treatment plan with the clinical response. Electrode positions in the numerical model were updated according to the actual positions during treatment. We compared the maximum value of the measured electric current with the current predicted by the model and good agreement was obtained. Finally, tumor coverage with an electric field above the reversible threshold was recalculated and determined to be approximately 94%. Therefore, according to the calculations, a small volume of tumor cells remained viable after electrochemotherapy, and these were sufficient for tumor regrowth.

Conclusions

In this, the first reported clinical case, deep-seated melanoma metastasis in the thigh of the patient was treated by electrochemotherapy, according to a treatment plan obtained by numerical modeling and optimization. Although only a partial response was obtained, the presented work demonstrates that treatment of deep-seated tumor nodules by electrochemotherapy is feasible and sets the ground for numerical treatment planning-based electrochemotherapy.

Trial registration

EudraCT:2008-008290-54

Electrodes for in vivo localised subcutaneous electropulsation and associated drug and nucleic acid delivery

BACKGROUND

Drug and nucleic acids can be delivered in vivo by an injection of the product followed by the application of a train of electric pulses.

OBJECTIVE

The success of the method is linked to the proper distribution of the electric field in the target tissue. This is under the control of the design of the electrodes.

METHODS

The field distribution can be obtained by computer simulation mainly by using numerical methods and simplifying hypothesis. The conclusions are validated by comparing the computed current and its experimental values on phantoms. A good agreement is obtained.

RESULTS/CONCLUSION

Targeting the delivery to the skin can be obtained by using an array of very short needle electrodes, by pinching the skin between two parallel plate electrodes, or by using contact wire electrodes.

Physiological effects of high- and low-voltage pulse combinations for gene electrotransfer in muscle

Gene transfer by electroporation is gaining momentum now that high-level, long-term expression of transgenes is being obtained. Several different pulse regimens are efficient, yet little information is available about the physiological muscular response to gene electrotransfer. This paper provides a comprehensive evaluation of the physiological and molecular effects on host tissue after DNA electrotransfer. We have tested several pulse regimens with special emphasis on the pulse combination of a short (100 microsec) high-voltage (HV) pulse followed by a long low-voltage (LV) pulse used for DNA electrotransfer, comparing it with 8 HV pulses designed to ensure extensive permeabilization of the muscle membrane. Using both mouse and rat skeletal muscle tissue, we investigated cell permeabilization by the 51Cr-labeled EDTA assay, lactate dehydrogenase release, Na+ and Ca2+ influx, K+ efflux, ATP release, and water content, as well as muscle function both in vivo and ex vivo, Hsp70 induction, and histology. In all these assays, the HVLV pulse combination gave rise to minimal disturbance of cell function, in all cases significantly different from results when using 8 HV pulses. The evaluated parameters were normalized after 1 week. The addition of DNA caused significantly more transmembrane exchange, and this may be due to entrance of the DNA through the membrane. In conclusion, this study comprehensively documents the immediate effects of DNA electrotransfer and shows that only slight cell disturbances occur with the HVLV pulses used for gene transfer. This is highly important, as minimal perturbation of cell physiology is essential for efficient transgene expression.

An e-learning application on electrochemotherapy

Background

Electrochemotherapy is an effective approach in local tumour treatment employing locally applied high-voltage electric pulses in combination with chemotherapeutic drugs. In planning and performing electrochemotherapy a multidisciplinary expertise is required and collaboration, knowledge and experience exchange among the experts from different scientific fields such as medicine, biology and biomedical engineering is needed. The objective of this study was to develop an e-learning application in order to provide the educational content on electrochemotherapy and its underlying principles and to support collaboration, knowledge and experience exchange among the experts involved in the research and clinics.

Methods

The educational content on electrochemotherapy and cell and tissue electroporation was based on previously published studies from molecular dynamics, lipid bilayers, single cell level and simplified tissue models to complex biological tissues and research and clinical results of electrochemotherapy treatment. We used computer graphics such as model-based visualization (i.e. 3D numerical modelling using finite element method) and 3D computer animations and graphical illustrations to facilitate the representation of complex biological and physical aspects in electrochemotherapy. The e-learning application is integrated into an interactive e-learning environment developed at our institution, enabling collaboration and knowledge exchange among the users. We evaluated the designed e-learning application at the International Scientific workshop and postgraduate course (Electroporation Based Technologies and Treatments). The evaluation was carried out by testing the pedagogical efficiency of the presented educational content and by performing the usability study of the application.

Results

The e-learning content presents three different levels of knowledge on cell and tissue electroporation. In the first part of the e-learning application we explain basic principles of electroporation process. The second part provides educational content about importance of modelling and visualization of local electric field in electroporation-based treatments. In the third part we developed an interactive module for visualization of local electric field distribution in 3D tissue models of cutaneous tumors for different parameters such as voltage applied, distance between electrodes, electrode dimension and shape, tissue geometry and electric conductivity. The pedagogical efficiency assessment showed that the participants improved their level of knowledge. The results of usability evaluation revealed that participants found the application simple to learn, use and navigate. The participants also found the information provided by the application easy to understand.

Conclusion

The e-learning application we present in this article provides educational material on electrochemotherapy and its underlying principles such as cell and tissue electroporation. The e-learning application is developed to provide an interactive educational content in order to simulate the "hands-on" learning approach about the parameters being important for successful therapy. The e-learning application together with the interactive e-learning environment is available to the users to provide collaborative and flexible learning in order to facilitate knowledge exchange among the experts from different scientific fields that are involved in electrochemotherapy. The modular structure of the application allows for upgrade with new educational content collected from the clinics and research, and can be easily adapted to serve as a collaborative e-learning tool also in other electroporation-based treatments such as gene electrotransfer, gene vaccination, irreversible tissue ablation and transdermal gene and drug delivery. The presented e-learning application provides an easy and rapid approach for information, knowledge and experience exchange among the experts from different scientific fields, which can facilitate development and optimisation of electroporation-based treatments.

The effects of the electric fields on hydrogels to achieve antitumoral drug release

The achievement of electrochemotherapy was obtained using electrodes covered with guar gum (GG) hydrogel swollen in a sulfate bleomycin solution. The bleomycin delivery into the plasma membranes of cancer cells occurs only when field strength (V/cm) was applied, decreasing the drug contact with healthy tissues. The effect of the delivered bleomycin at different concentrations was examined on tumoral mouse fibroblast (NIH3T3) and human coronary artery endothelial cells. The GG hydrogel released the drug only when the field strength was applied and the amount depended on the electromotive force. Consequently, cellular survival depended on the field strength. Moreover in vitro results showed a bigger cellular mortality of the NIH3T3 compared with endothelial cells. The best parameters to be utilized in electrochemotherapy were ascertained.

Electric pulses used in electrochemotherapy and electrogene therapy do not significantly change the expression profile of genes involved in the development of cancer in malignant melanoma cells

Background

Electroporation is a versatile method for in vitro or in vivo delivery of different molecules into cells. However, no study so far has analysed the effects of electric pulses used in electrochemotherapy (ECT pulses) or electric pulses used in electrogene therapy (EGT pulses) on malignant cells. We studied the effect of ECT and EGT pulses on human malignant melanoma cells in vitro in order to understand and predict the possible effect of electric pulses on gene expression and their possible effect on cell behaviour.

Methods

We used microarrays with 2698 different oligonucleotides to obtain the expression profile of genes involved in apoptosis and cancer development in a malignant melanoma cell line (SK-MEL28) exposed to ECT pulses and EGT pulses.

Results

Cells exposed to ECT pulses showed a 68.8% average survival rate, while cells exposed to EGT pulses showed a 31.4% average survival rate. Only seven common genes were found differentially expressed in cells 16 h after exposure to ECT and EGT pulses. We found that ECT and EGT pulses induce an HSP70 stress response mechanism, repress histone protein H4, a major protein involved in chromatin assembly, and down-regulate components involved in protein synthesis.

Conclusion

Our results show that electroporation does not significantly change the expression profile of major tumour suppressor genes or oncogenes of the cell cycle. Moreover, electroporation also does not changes the expression of genes involved in the stability of DNA, supporting current evidence that electroporation is a safe method that does not promote tumorigenesis. However, in spite of being considered an isothermal method, it does to some extent induce stress, which resulted in the expression of the environmental stress response mechanism, HSP70.

The effect of high frequency steep pulsed electric fields on in vitro and in vivo antitumor efficiency of ovarian cancer cell line skov3 and potential use in electrochemotherapy

BACKGROUND

Patients received electrochemotherapy often associated with unpleasant sensations mainly result from low-frequency electric pulse induced muscle contractions. Increasing the repetition frequency of electric pulse can reduce unpleasant sensations. However, due to the specificity of SPEF, frequency related antitumor efficiency need to be further clarified. The aim of this study was to compare in vitro cytotoxic and in vivo antitumor effect on ovarian cancer cell line SKOV3 by SPEF with different repetition frequencies. Explore potential benefits of using high frequency SPEF in order to be exploitable in electrochemotherapy.

METHODS

For in vitro experiment, SKOV3 cell suspensions were exposed to SPEF with gradient increased frequencies (1, 60, 1000, 5000 Hz) and electric field intensity (50, 100, 150, 200, 250, 300, 350, 400 V/cm) respectively. For in vivo test, SKOV3 subcutaneous implanted tumor in BALB/c nude mice (nu/nu) were exposure to SPEF with gradient increased frequencies (1, 60, 1000, 5000 Hz) and fixed electric field intensity (250 V/cm) (7 mice for each frequency and 7 for control). Antitumor efficiency was performed by in vitro cytotoxic assay and in vivo tumor growth inhibition rate, supplemented by histological and TEM observations. Data were analyzed using one-way ANOVA followed by the comparisons of multiple groups.

RESULTS

SPEF with a given frequency and appropriate electric field intensity could achieve similar cytotoxicity until reached a plateau of maximum cytotoxicity (approx. 100%). SPEF with different frequencies had significant antitumor efficiency in comparison to the control group (P < 0.05). However, there was no difference in tumor responses among test groups (P > 0.05). Histological and TEM observations demonstrated obvious cell damages in response to SPEF exposure. Furthermore, SPEF with 5 kHz could induce apoptosis under TEM observations both in vitro and in vivo.

CONCLUSION

SPEF with high frequency could also achieve similar antitumor efficiency which can be used to reduce unpleasant sensations in tumor electrical treatment. Our research proposed potential applications of using high frequency SPEF in clinical cancer treatment.

Physical methods of nucleic acid transfer: general concepts and applications

Physical methods of gene (and/or drug) transfer need to combine two effects to deliver the therapeutic material into cells. The physical methods must induce reversible alterations in the plasma membrane to allow the direct passage of the molecules of interest into the cell cytosol. They must also bring the nucleic acids in contact with the permeabilized plasma membrane or facilitate access to the inside of the cell. These two effects can be achieved in one or more steps, depending upon the methods employed. In this review, we describe and compare several physical methods: biolistics, jet injection, hydrodynamic injection, ultrasound, magnetic field and electric pulse mediated gene transfer. We describe the physical mechanisms underlying these approaches and discuss the advantages and limitations of each approach as well as its potential application in research or in preclinical and clinical trials. We also provide conclusions, comparisons, and projections for future developments. While some of these methods are already in use in man, some are still under development or are used only within clinical trials for gene transfer. The possibilities offered by these methods are, however, not restricted to the transfer of genes and the complementary uses of these technologies are also discussed. As these methods of gene transfer may bypass some of the side effects linked to viral or biochemical approaches, they may find their place in specific clinical applications in the future.

Importance of contact surface between electrodes and treated tissue in electrochemotherapy

Electrochemotherapy is an effective antitumor treatment employing locally applied high voltage electric pulses delivered through conductive electrodes to the tumor in combination with chemotherapeutic drugs. The efficiency of electrochemotherapy strongly depends on the local electric field distribution inside the target tissue. For successful therapy the entire target tissue has to be exposed to the local electric field strength above the reversible threshold. The aim of this study is to demonstrate the influence of the contact surface between electrode and treated tissue on the coverage of the tumor tissue by sufficiently high local electric field. The electric field distribution is calculated by means of numerical modeling using finite element method. Numerical results are confirmed with in vivo experiments. We demonstrated that the placement of electrodes giving larger electrode-tissue contact surface leads to improved electrochemotherapy outcome. Our results provide guidance on electrochemotherapy for treatment of protruding cutaneous tumors using parallel plate electrodes.

Electrochemotherapy in veterinary oncology

Electropermeabilization is a method that uses electric field pulses to induce an electrically mediated reorganization of the plasma membrane of cells. Electrochemotherapy combines local or systemic administration of chemotherapeutic drugs such as bleomycin or cisplatin that have poor membrane permeability with electropermeabilization by direct application of electric pulses to the tumors. Preclinical studies have demonstrated excellent antitumor effectiveness of electrochemotherapy on different animal models and various tumor types, minimal toxicity, and safety of the procedure. Based on results of preclinical studies, clinical studies were conducted in human patients, which demonstrated pronounced antitumor effectiveness of electrochemotherapy with 80-85% objective responses of the treated cutaneous and SC tumors. Clinical studies in veterinary oncology have demonstrated that electrochemotherapy is very effective in the treatment of cutaneous and SC tumors of different histologic types in cats, dogs, and horses. The results of these studies have also demonstrated approximately 80% long-lasting objective responses of tumors treated by electrochemotherapy. Primary tumors of different histologic types were treated. Electrochemotherapy in veterinary oncology has future promise to be highly effective, and could be used to treat primary or recurrent solitary or multiple cutaneous and SC tumors of different histology or as an adjuvant treatment to surgery.

Tumor destruction using electrochemotherapy followed by CpG oligodeoxynucleotide injection induces distant tumor responses

PURPOSE

Electrochemotherapy (ECT) is an effective local therapy of human cutaneous cancers but has no effect on distant untreated tumors. We addressed whether tumor-associated antigens released after ECT could induce an efficient systemic immunity when associated with an appropriate immunoadjuvant.

METHODS AND RESULTS

We first studied the nature of the cellular recruitment and the expression of various toll-like receptors (TLRs) in tumors treated by ECT. We found that ECT induced a massive recruitment of CD11c and CD11b positive cells in the tumors and a strong increase of TLR9 expression. We then tested antitumor effects of the combination: ECT followed by TLR-9 ligands, CpG oligodeoxynucleotides (CpG ODN), in three murine tumor models. We found that this combination triggered both potent local synergistic antitumor effects, on the ipsi-lateral ECT-treated tumor, and more interestingly, a systemic antitumor response on the contra-lateral untreated tumor, in the three models. The systemic protection was T-cell dependent as it was not observed in nude littermates. The combination induced tumor-specific T cell effectors in the tumor-draining lymph nodes and in the spleen which secreted significantly more gamma-interferon upon activation than with ECT or CpG ODN alone.

CONCLUSIONS

Our data show that ECT and CpG ODN synergize and induce a significant increase of the local effect and a systemic T-dependent antitumor response. Such combination constitutes a potential innovative vaccination strategy using in situ tumor-associated antigens that could eventually be translated into the clinic.

The effect of electroporation pulses on functioning of the heart

Electrochemotherapy is an effective antitumor treatment currently applied to cutaneous and subcutaneous tumors. Electrochemotherapy of tumors located close to the heart could lead to adverse effects, especially if electroporation pulses were delivered within the vulnerable period of the heart or if they coincided with arrhythmias of some types. We examined the influence of electroporation pulses on functioning of the heart of human patients by analyzing the electrocardiogram. We found no pathological morphological changes in the electrocardiogram; however, we demonstrated a transient RR interval decrease after application of electroporation pulses. Although no adverse effects due to electroporation have been reported so far, the probability for complications could increase in treatment of internal tumors, in tumor ablation by irreversible electroporation, and when using pulses of longer durations. We evaluated the performance of our algorithm for synchronization of electroporation pulse delivery with electrocardiogram. The application of this algorithm in clinical electroporation would increase the level of safety for the patient and suitability of electroporation for use in anatomical locations presently not accessible to existing electroporation devices and electrodes.

Therapy for Unresectable Recurrent and In-Transit Extremity Melanoma

Background

Unresectable recurrent and in-transit extremity melanoma presents a dilemma for the treating physician. While the disease is confined to the involved limb, the survival mimics that of multiple nodal metastases, with a 10-year survival rate of approximately 40%. This represents late-stage disease for which curative treatment options are limited.

Methods

To review the current treatment strategies for stage IIIB (N2c) in-transit and recurrent melanoma focusing on the options for unresectable disease, MEDLINE was searched for studies of known and experimental treatments for in-transit and recurrent extremity melanoma. Further results were obtained after review of the initial citations.

Results

For unresectable recurrences and in-transit metastases, therapies are limited to palliative (radiation), local (intratumoral injection, laser ablation and electroporation), regional (isolated limb perfusion/infusion), and systemic (chemotherapy) when local or regional techniques are not feasible.

Conclusions

In this patient population, intratumoral techniques have a limited role with current treatment regimens, but with the development of new drugs, these techniques may have more utility. If not contraindicated, regional techniques provide the greatest control and have minimal operative morbidity. Until new regimens are available, systemic therapy continues to be associated with considerable toxicity and only marginal response rates.

Kinetics of transmembrane transport of small molecules into electropermeabilized cells

The transport of propidium iodide into electropermeabilized Chinese hamster ovary cells was monitored with a photomultiplier tube during and after the electric pulse. The influence of pulse amplitude and duration on the transport kinetics was investigated with time resolutions from 200 ns to 4 ms in intervals from 400 micros to 8 s. The transport became detectable as early as 60 micros after the start of the pulse, continued for tens of seconds after the pulse, and was faster and larger for higher pulse amplitudes and/or longer pulse durations. With fixed pulse parameters, transport into confluent monolayers of cells was slower than transport into suspended cells. Different time courses of fluorescence increase were observed during and at various times after the pulse, reflecting different transport mechanisms and ongoing membrane resealing. The data were compared to theoretical predictions of the Nernst-Planck equation. After a delay of 60 micros, the time course of fluorescence during the pulse was approximately linear, supporting a mainly electrophoretic solution of the Nernst-Planck equation. The time course after the pulse agreed with diffusional solution of the Nernst-Planck equation if the membrane resealing was assumed to consist of three distinct components, with time constants in the range of tens of microseconds, hundreds of microseconds, and tens of seconds, respectively.

Efficient electrotransfection into canine muscle

Two different types of electroporation protocols have been developed for efficient electrotransfer of plasmid DNA into skeletal muscle of experimental animals. At first, only low voltage electric pulses have been used, but lately, a combination of high and low voltage pulses has been suggested as more efficient. Up to date, in dogs, this type of electroporation protocol has never been used for muscle targeted plasmid DNA electrotransfection. In this study, we used two different DNA plasmids, one encoding green fluorescent protein and one encoding human interleukin-12. Five different electroporation protocols were evaluated. Three of them featured different combinations of high and low voltage pulses, and two were performed with delivery of low voltage pulses only. Our study shows that combination of 1 high voltage pulse (600 V/cm, 100 mus), followed by 4 low voltage pulses (80 V/cm, 100 ms, 1 Hz) yielded in the same transfection efficiency as the standard trains of low voltage pulses. However, this protocol is performed quicker and, thus, more suitable for potential use in clinical practice. In addition, it yielded in detectable systemic expression of human interleukin-12. Electrotransfer of either of the plasmids was associated with only mild and transitory local side effects, without clinically detectable systemic side effects. The results indicate that electrotransfection is a feasible, effective, and safe method for muscle targeted gene therapy in dogs, which could have potential for clinical applications in veterinary medicine of small animals.

Theoretical and experimental analysis of conductivity, ion diffusion and molecular transport during cell electroporation--relation between short-lived and long-lived pores

Electroporation is usually described as a formation of transient pores in the cell membrane in the presence of a strong electric field, which enables transport of molecules and ions across the cell membrane. Several experimental studies of electroporation showed a complex dependence of the transport on pulse parameters. In only few studies, however, the actual transport across the membrane was quantified. Current theoretical studies can describe pore formation in artificial lipid membranes but still cannot explain mechanisms of formation and properties of long-lived pores which are formed during cell electroporation. The focus of our study is to connect theoretical description of pore formation during the electric pulses with experimental observation of increased transport after the pulses. By analyzing transient increase in conductivity during the pulses in parallel with ion efflux after the pulses the relation between short-lived and long-lived pores was investigated. We present a simple model that incorporates an increase in the fraction of long-lived pores with higher electric field due to larger area of the cell membrane exposed to above-critical voltage and due to higher energy which is available for pore formation. We also show that each consecutive pulse increases the probability for the formation of long-lived pores.

Electrode commutation sequence for honeycomb arrangement of electrodes in electrochemotherapy and corresponding electric field distribution

Electrochemotherapy is a treatment based on combination of chemotherapeutic drug and electroporation. It is used in clinics for treatment of solid tumours. For electrochemotherapy of larger tumours multiple needle electrodes were already suggested. We developed and tested electrode commutation circuit, which controls up to 19 electrodes independently. Each electrode can be in one of three possible states: on positive or negative potential or in the state of high impedance. In addition, we tested a pulse sequence using seven electrodes for which we also calculated electric field distribution in tumour tissue by means of finite-elements method. Electrochemotherapy, performed by multiple needle electrodes and tested pulse sequence on large subcutaneous murine tumour model resulted in tumour growth delay and 57% complete responses, thus demonstrating that the tested electrode commutation sequence is efficient.

Vascular disrupting action of electroporation and electrochemotherapy with bleomycin in murine sarcoma

Electrochemotherapy has a direct cytotoxic effect on tumour cells, and presumably, a vascular disrupting effect. In this study, on the basis of the prediction of the mathematical model, histological evaluation and physiological measurements of the tumours were carried out to confirm that electroporation and electrochemotherapy of tumours have a vascular disrupting action. In the study, SA-1 solid subcutaneous sarcoma tumours in A/J mice were treated by bleomycin (BLM) given intravenously (1 mg kg(-1)), application of electric pulses (8 pulses, 1040 V, 100 micros, 1 Hz) or a combination of both - electrochemotherapy. The vascular effect was determined by laser Doppler flowmetry, power Doppler ultrasonographic imaging and Patent blue staining. The extent of tumour hypoxia was determined immunohistochemically by hypoxia marker pimonidazole and partial pressure of oxygen (pO(2)) in tumours by electron paramagnetic resonance oximetry. Electrochemotherapy with BLM induced good antitumour effect with 22 days, tumour growth delay and 38% tumour cures. The application of electric pulses to the tumours induced instant but transient tumour blood flow reduction (for 70%) that was recovered in 24 h. During this tumour blood flow reduction, we determined an increase in hypoxic tumour area for up to 30%, which was also reflected in reduced tumour oxygenation (for 70%). According to the described mathematical model, endothelial cells lining in tumour blood vessels are exposed to a approximately 40% higher electric field than the surrounding tumour cells, and therefore easily electroporated, allowing access of high BLM concentration to the cytosol. Consequently, electrochemotherapy has, besides the immediate vascular disrupting action, also a delayed one (after 24 h), as a consequence of endothelial cell swelling and apoptosis demonstrated by extensive tumour necrosis, tumour hypoxia, prolonged reduction of tumour blood flow and significant tumour growth delay, and tumour cures. Our results demonstrate that in addition to the well-established direct cytotoxic effect on tumour cells, electrochemotherapy also has an indirect vascular disrupting action resulting altogether in extensive tumour cell necrosis leading to complete regression of tumours.

Application of electroporation gene therapy: past, current, and future

Twenty-five years after the publication of the first report on gene transfer in vitro in cultured cells by the means of electric pulse delivery, reversible cell electroporation for gene transfer and gene therapy (DNA electrotransfer) is at a crossroad in its development. Present knowledge on the effects of cell exposure to appropriate electric field pulses, particularly at the level of the cell membrane, is reported here as an introduction to the large range of applications described in this book. The importance of the models of electric field distribution in tissues and of the correct choice of electrodes and applied voltages is highlighted. The mechanisms involved in DNA electrotransfer, which include cell electropermeabilization and DNA electrophoresis, are also surveyed. The feasibility of electric pulse for gene transfer in humans is discussed taking into account that electric pulse delivery is already regularly used for localized drug delivery in the treatment of cutaneous and subcutaneous solid tumors by electrochemotherapy. Because recent technological developments have made DNA electrotransfer more efficient and safer, this nonviral gene therapy approach is now ready to reach the clinical stage. A good understanding of DNA electrotransfer principles and a respect for safe procedures will be key elements for the successful future transition of DNA electrotransfer to the clinics.

Electroporation for drug and gene delivery in the clinic: doctors go electric

Electroporation is a unique system for drug and gene delivery, as it is possible to very specifically target certain tissues within the body with whatever drug, gene, isotope, or other product is desired in a specific situation. An increasing number of clinical trials are being launched, and sophistication of equipment and protocols continues. This chapter reviews present knowledge from clinical trials, describes important issues in the patient management when using electroporation, and outlines future perspectives of the technology.

Tumor ablation with irreversible electroporation

We report the first successful use of irreversible electroporation for the minimally invasive treatment of aggressive cutaneous tumors implanted in mice. Irreversible electroporation is a newly developed non-thermal tissue ablation technique in which certain short duration electrical fields are used to permanently permeabilize the cell membrane, presumably through the formation of nanoscale defects in the cell membrane. Mathematical models of the electrical and thermal fields that develop during the application of the pulses were used to design an efficient treatment protocol with minimal heating of the tissue. Tumor regression was confirmed by histological studies which also revealed that it occurred as a direct result of irreversible cell membrane permeabilization. Parametric studies show that the successful outcome of the procedure is related to the applied electric field strength, the total pulse duration as well as the temporal mode of delivery of the pulses. Our best results were obtained using plate electrodes to deliver across the tumor 80 pulses of 100 micros at 0.3 Hz with an electrical field magnitude of 2500 V/cm. These conditions induced complete regression in 12 out of 13 treated tumors, (92%), in the absence of tissue heating. Irreversible electroporation is thus a new effective modality for non-thermal tumor ablation.

Analytical and numerical quantification and comparison of the local electric field in the tissue for different electrode configurations

BACKGROUND

Electrochemotherapy and gene electrotransfer are novel promising treatments employing locally applied high electric pulses to introduce chemotherapeutic drugs into tumor cells or genes into target cells based on the cell membrane electroporation. The main focus of this paper was to calculate analytically and numerically local electric field distribution inside the treated tissue in two dimensional (2D) models for different plate and needle electrode configurations and to compare the local electric field distribution to parameter U/d, which is widely used in electrochemotherapy and gene electrotransfer studies. We demonstrate the importance of evaluating the local electric field distribution in electrochemotherapy and gene electrotransfer.

METHODS

We analytically and numerically analyze electric field distribution based on 2D models for electrodes and electrode configurations which are most widely used in electrochemotherapy and gene electrotransfer. Analytical calculations were performed by solving the Laplace equation and numerical calculations by means of finite element method in two dimensions.

RESULTS

We determine the minimal and maximal E inside the target tissue as well as the maximal E over the entire treated tissue for the given electrode configurations. By comparing the local electric field distribution calculated for different electrode configurations to the ratio U/d, we show that the parameter U/d can differ significantly from the actual calculated values of the local electric field inside the treated tissue. By calculating the needed voltage to obtain E > U/d inside the target tissue, we showed that better electric field distribution can be obtained by increasing the number and changing the arrangement of the electrodes.

CONCLUSION

Based on our analytical and numerical models of the local electric field distribution we show that the applied voltage, configuration of the electrodes and electrode position need to be chosen specifically for each individual case, and that numerical modeling can be used to optimize the appropriate electrode configuration and adequate voltage. Using numerical models we further calculate the needed voltage for a specific electrode configuration to achieve adequate E inside the target tissue while minimizing damages of the surrounding tissue. We present also analytical solutions, which provide a convenient, rapid, but approximate method for a pre-analysis of electric field distribution in treated tissue.

A study of the immunological response to tumor ablation with irreversible electroporation

Immune cell recruitment during the treatment of sarcoma tumors in mice with irreversible electroporation was studied by immunohistochemistry. Irreversible electroporation is a non-thermal tissue ablation technique in which certain short duration electrical fields are used to permanently permeabilize the cell membrane, presumably through the formation of nanoscale defects in the membrane. Employing irreversible electroporation parameters known to completely ablate the tumors without thermal effects we did not find infiltration of immune cells probably because of the destruction of infiltration routes. We confirm here that immune response is not instrumental in irreversible electroporation efficacy, and we propose that irreversible electroporation may be, therefore, a treatment modality of interest to immunodepressed cancer patients.

Electrochemotherapy in treatment of tumours

AIM

Electrochemotherapy is a local drug delivery approach aimed at treatment with palliative intent of cutaneous and subcutaneous tumour nodules of different histologies. Electrochemotherapy, via cell membrane permeabilising electric pulses, potentiates the cytotoxicity of non-permeant or poorly permeant anticancer drugs with high intrinsic cytotoxicity, such as bleomycin or cisplatin, at the site of electric pulse application.

METHODS

An overview of preclinical and clinical studies is presented, and the treatment procedure is further critically evaluated.

RESULTS

In clinical studies electrochemotherapy has proved to be a highly efficient and safe approach for treating cutaneous and subcutaneous tumour nodules. The treatment response for various tumours (predominantly melanoma) was approximately 75% complete and 10% partial response of the treated nodules.

CONCLUSIONS

Electrochemotherapy is a new, clinically acknowledged method for the treatment of cutaneous and subcutaneous tumours. Its advantages are high effectiveness on tumours with different histologies, simple application, minimal side effects and the possibility of effective repetitive treatment.

Electroporator with automatic change of electric field direction improves gene electrotransfer in-vitro

Background

Gene electrotransfer is a non-viral method used to transfer genes into living cells by means of high-voltage electric pulses. An exposure of a cell to an adequate amplitude and duration of electric pulses leads to a temporary increase of cell membrane permeability. This phenomenon, termed electroporation or electropermeabilization, allows various otherwise non-permeant molecules, including DNA, to cross the membrane and enter the cell. The aim of our research was to develop and test a new system and protocol that would improve gene electrotransfer by automatic change of electric field direction between electrical pulses.

Methods

For this aim we used electroporator (EP-GMS 7.1) and developed new electrodes. We used finite-elements method to calculate and evaluate the electric field homogeneity between these new electrodes. Quick practical test was performed on confluent cell culture, to confirm and demonstrate electric field distribution. Then we experimentally evaluated the effectiveness of the new system and protocols on CHO cells. Gene transfection and cell survival were evaluated for different electric field protocols.

Results

The results of in-vitro gene electrotransfer experiments show that the fraction of transfected cells increases by changing the electric field direction between electrical pulses. The fluorescence intensity of transfected cells and cell survival does not depend on electric field protocol. Moreover, a new effect a shading effect was observed during our research. Namely, shading effect is observed during gene electrotransfer when cells are in clusters, where only cells facing negative electro-potential in clusters become transfected and other ones which are hidden behind these cells do not become transfected.

Conclusion

On the basis of our results we can conclude that the new system can be used in in-vitro gene electrotransfer to improve cell transfection by changing electric field direction between electrical pulses, without affecting cell survival.

Sensitive and precise regulation of haemoglobin after gene transfer of erythropoietin to muscle tissue using electroporation

Electroporation-based gene transfer (electro gene transfer (EGT)) is gaining increasing momentum, in particular for muscle tissue, where long-term high-level expression is obtainable. Induction of expression using the Tet-On system was previously established; however, attempts to reach a predefined target dose - a prescription, have not been reported. We set three target haemoglobin levels (10, 12 and 14 mmol/l, base level was 8.2 mmol/l) and aimed at them by transferring the erythropoietin (EPO) gene to mouse tibialis cranialis (TC) muscle, and varying (1) DNA amount, (2) muscle mass transfected and (3) induction with the Tet-On system. Results showed that (a) using GFP, luciferase and EPO low DNA amounts were needed. In fact, 0.5 microg of DNA to one TC muscle led to significant Hgb elevation - this amount extrapolates to 1.4 mg of DNA in humans, (b) three prescribers hit the targets with average Hgb of 10.5, 12.0 and 13.7 mmol/l, (c) different approaches could be used, (d) undershooting could be corrected by retransferring, and (e) overshooting could be alleviated by reducing dose of inducer (doxycycline (dox)). In conclusion, this study shows that using EGT to muscle, a preset level of protein expression can be reached. This is of great interest for future clinical use.