Numerical optimization of gene electrotransfer into muscle tissue

<p>Abstract</p> <p>Background</p> <p>Electroporation-based gene therapy and DNA vaccination are promising medical applications that depend on transfer of pDNA into target tissues with use of electric pulses. Gene electrotransfer efficiency depends on electrode configuration and electric pulse parameters, which determine the electric field distribution. Numerical modeling represents a fast and convenient method for optimization of gene electrotransfer parameters. We used numerical modeling, parameterization and numerical optimization to determine the optimum parameters for gene electrotransfer in muscle tissue.</p> <p>Methods</p> <p>We built a 3D geometry of muscle tissue with two or six needle electrodes (two rows of three needle electrodes) inserted. We performed a parametric study and optimization based on a genetic algorithm to analyze the effects of distances between the electrodes, depth of insertion, orientation of electrodes with respect to muscle fibers and applied voltage on the electric field distribution. The quality of solutions were evaluated in terms of volumes of reversibly (desired) and irreversibly (undesired) electroporated muscle tissue and total electric current through the tissue.</p> <p>Results</p> <p>Large volumes of reversibly electroporated muscle with relatively little damage can be achieved by using large distances between electrodes and large electrode insertion depths. Orienting the electrodes perpendicular to muscle fibers is significantly better than the parallel orientation for six needle electrodes, while for two electrodes the effect of orientation is not so pronounced. For each set of geometrical parameters, the window of optimal voltages is quite narrow, with lower voltages resulting in low volumes of reversibly electroporated tissue and higher voltages in high volumes of irreversibly electroporated tissue. Furthermore, we determined which applied voltages are needed to achieve the optimal field distribution for different distances between electrodes.</p> <p>Conclusion</p> <p>The presented numerical study of gene electrotransfer is the first that demonstrates optimization of parameters for gene electrotransfer on tissue level. Our method of modeling and optimization is generic and can be applied to different electrode configurations, pulsing protocols and different tissues. Such numerical models, together with knowledge of tissue properties can provide useful guidelines for researchers and physicians in selecting optimal parameters for <it>in vivo </it>gene electrotransfer, thus reducing the number of animals used in studies of gene therapy and DNA vaccination.</p

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

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

An e-learning application on electrochemotherapy

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Modeling and visualization of electropermeabilization of biological tissues exposed to high-voltage electric pulses

In vivo electroporation is used as an effective and safe tool for administration of a variety of extracellular agents such as chemotherapeutic drugs (e.g. bleomycin), DNA or other molecules, which in normal conditions do not cross the cell membrane, into many different target tissue cells. The main focus of the present doctoral theses is the analysis of in vivo electroporation and corresponding local electric field distribution used in electrochemotherapy and electroporation based gene therapy and vaccination. The aims of this doctoral thesis cover three important issues in the development of electroporation based technologies and treatments: development of realistic numerical models of different tissues (i.e. muscle, tumor and skin) and calculations and visualization of local electric field distribution in the models; validation of the realistic numerical models by in vivo experiments and development of a web-based interactive e-learning application on electroporation of cells and tissues and on electroporation based therapies and treatments. (e.g. clinical electrochemotherapy of tumors and gene electrotransfer).L efficacité des traitements médicaux, tel que électrochimiothérapie et la thérapie génique non-virale par électrotransfer d'ADN, est due à l électroperméabilisation des cellules constituant le tissue ciblé par un champ électrique local d intensité supérieure à une valeur seuil réversible. Une cellule électropermeabilisée est ainsi plus sensible à un médicament cytotoxique (e.g. la bléomycine) aussi bien qu aux molécules de l ADN. La première partie de la thèse s est intéressée aux modèles mathématiques des tissues ciblés afin de visualiser la distribution du champ électrique local par des simulations numériques, ce qui permet d optimiser le choix du type d électrodes à utiliser et l amplitude du voltage à appliquer de telle sorte qu une thérapie basée sur l électroperméabilisation soit la plus efficace possible. La deuxième partie expérimentale a consisté à valider les modelés mathématiques par des expériences in vivo chez les animaux. La dernière troisième partie de la thèse concerne le développement d une application internet pour la formation à distance sur les mécanismes de l électroperméabilisation au niveau des cellules et des tissus.CHATENAY M.-PARIS 11-BU Pharma. (920192101) / SudocSudocFranceF

Modeling of Microvascular Permeability Changes after Electroporation

<div><p>Vascular endothelium selectively controls the transport of plasma contents across the blood vessel wall. The principal objective of our preliminary study was to quantify the electroporation-induced increase in permeability of blood vessel wall for macromolecules, which do not normally extravasate from blood into skin interstitium in homeostatic conditions. Our study combines mathematical modeling (by employing pharmacokinetic and finite element modeling approach) with <i>in vivo</i> measurements (by intravital fluorescence microscopy). Extravasation of fluorescently labeled dextran molecules of two different sizes (70 kDa and 2000 kDa) following the application of electroporation pulses was investigated in order to simulate extravasation of therapeutic macromolecules with molecular weights comparable to molecular weight of particles such as antibodies and plasmid DNA. The increase in blood vessel permeability due to electroporation and corresponding transvascular transport was quantified by calculating the apparent diffusion coefficients for skin microvessel wall (D [μm²/s]) for both molecular sizes. The calculated apparent diffusion coefficients were D = 0.0086 μm²/s and D = 0.0045 μm²/s for 70 kDa and 2000 kDa dextran molecules, respectively. The results of our preliminary study have important implications in development of realistic mathematical models for prediction of extravasation and delivery of large therapeutic molecules to target tissues by means of electroporation.</p></div

Sensitivity analysis of the calculated apparent diffusion coefficient <i>D</i>_<i>wall</i>.

<p>Sensitivity analysis of apparent diffusion coefficient <i>D</i>_<i>wall</i> for 70 kDa and 2000 kDa FD to the values of <i>D</i>_<i>tiss</i> over the range from 2 μm²/s to 70 μm²/s. <i>D</i>_<i>wall</i>(<i>D</i>_<i>tiss</i>) functions calculated for 70 kDa and 2000 kDa FD are represented with red and blue curves, respectively. The bold curves represent the median values of <i>D</i>_<i>wall</i>.</p

The modeled infinite geometry of skin and capillaries.

<p>Infinite geometry is created by infinitely repeating the grayed-out region which we realized in Comsol Multiphysics by applying boundary conditions of symmetry at the inner boundaries 2 and 3. The height of the skin layer was <i>H</i> = 300 μm. The radius of microvessels was <i>r</i> = 3.5 μm. The distance from the skin surface to the capillaries was <i>h</i> = 72 μm. The distance between the centers of neighboring capillaries was <i>a</i> = 60 μm. The thickness of capillary wall was <i>w</i> = 1 μm. The distance between electrodes was <i>d</i> = 6mm.</p