Nahuel Manuel Olaiz

The Role of pH Fronts in Reversible Electroporation

We present experimental measurements and theoretical predictions of ion transport in agar gels during reversible electroporation (ECT) for conditions typical to many clinical studies found in the literature, revealing the presence of pH fronts emerging from both electrodes. These results suggest that pH fronts are immediate and substantial. Since they might give rise to tissue necrosis, an unwanted condition in clinical applications of ECT as well as in irreversible electroporation (IRE) and in electrogenetherapy (EGT), it is important to quantify their extent and evolution. Here, a tracking technique is used to follow the space-time evolution of these pH fronts. It is found that they scale in time as , characteristic of a predominantly diffusive process. Comparing ECT pH fronts with those arising in electrotherapy (EChT), another treatment applying constant electric fields whose main goal is tissue necrosis, a striking result is observed: anodic acidification is larger in ECT than in EChT, suggesting that tissue necrosis could also be greater. Ways to minimize these adverse effects in ECT are suggested.

The Role of Ph Fronts in Tissue Electroporation Based Treatments

Treatments based on electroporation (EP) induce the formation of pores in cell membranes due to the application of pulsed electric fields. We present experimental evidence of the existence of pH fronts emerging from both electrodes during treatments based on tissue EP, for conditions found in many studies, and that these fronts are immediate and substantial. pH fronts are indirectly measured through the evanescence time (ET), defined as the time required for the tissue buffer to neutralize them. The ET was measured through a pH indicator imaged at a series of time intervals using a four-cluster hard fuzzy-c-means algorithm to segment pixels corresponding to the pH indicator at every frame. The ET was calculated as the time during which the number of pixels was 10% of those in the initial frame. While in EP-based treatments such as reversible (ECT) and irreversible electroporation (IRE) the ET is very short (though enough to cause minor injuries) due to electric pulse characteristics and biological buffers present in the tissue, in gene electrotransfer (GET), ET is much longer, enough to denaturate plasmids and produce cell damage. When any of the electric pulse parameters is doubled or tripled the ET grows and, remarkably, when any of the pulse parameters in GET is halved, the ET drops significantly. Reducing pH fronts has relevant implications for GET treatment efficiency, due to a substantial reduction of plasmid damage and cell loss.

The role of additional pulses in electropermeabilization protocols.

Electropermeabilization (EP) based protocols such as those applied in medicine, food processing or environmental management, are well established and widely used. The applied voltage, as well as tissue electric conductivity, are of utmost importance for assessing final electropermeabilized area and thus EP effectiveness. Experimental results from literature report that, under certain EP protocols, consecutive pulses increase tissue electric conductivity and even the permeabilization amount. Here we introduce a theoretical model that takes into account this effect in the application of an EP-based protocol, and its validation with experimental measurements. The theoretical model describes the electric field distribution by a nonlinear Laplace equation with a variable conductivity coefficient depending on the electric field, the temperature and the quantity of pulses, and the Pennes Bioheat equation for temperature variations. In the experiments, a vegetable tissue model (potato slice) is used for measuring electric currents and tissue electropermeabilized area in different EP protocols. Experimental measurements show that, during sequential pulses and keeping constant the applied voltage, the electric current density and the blackened (electropermeabilized) area increase. This behavior can only be attributed to a rise in the electric conductivity due to a higher number of pulses. Accordingly, we present a theoretical modeling of an EP protocol that predicts correctly the increment in the electric current density observed experimentally during the addition of pulses. The model also demonstrates that the electric current increase is due to a rise in the electric conductivity, in turn induced by temperature and pulse number, with no significant changes in the electric field distribution. The EP model introduced, based on a novel formulation of the electric conductivity, leads to a more realistic description of the EP phenomenon, hopefully providing more accurate predictions of treatment outcomes.

Tissue damage modeling in gene electrotransfer: the role of pH.

Optimal gene electrotransfer (GET) requires a compromise between maximum transgene expression and minimal tissue damage. GET in skeletal muscle can be improved by pretreatment with hyaluronidase which contributes to maximize transgene uptake and expression. Nevertheless, tissue damage remains severe close to the electrodes, with a concomitant loss of GET efficiency. Here we analyze the role of pH in tissue damage in GET protocols through in vivo modeling using a transparent chamber implanted into the dorsal skinfold of a mouse (DSC) and intravital microscopy, and in silico modeling using the Poisson-Nernst-Planck equations for ion transport. DSC intravital microscopy reveals the existence of pH fronts emerging from both electrodes and that these fronts are immediate and substantial thus giving rise to tissue necrosis. Theoretical modeling confirms experimental measurements and shows that in GET protocols whether with or without hyaluronidase pretreatment, pH fronts are the principal cause of muscle damage near the electrodes. It also predicts that an optimal efficiency in GET protocols, that is a compromise between obtaining maximum electroporated area and minimal tissue damage, is achieved when the electric field applied is near 183 V/cm in a GET protocol and 158 V/cm in a hyaluronidase+GET protocol.

Combined local and systemic bleomycin administration in electrochemotherapy to reduce the number of treatment sessions.

Background Electrochemotherapy (ECT), a medical treatment widely used in human patients for tumor treatment, increases bleomycin toxicity by 1000 fold in the treated area with an objective response rate of around 80%. Despite its high response rate, there are still 20% of cases in which the patients are not responding. This could be ascribed to the fact that bleomycin, when administered systemically, is not reaching the whole tumor mass properly because of the characteristics of tumor vascularization, in which case local administration could cover areas that are unreachable by systemic administration. Patients and methods We propose combined bleomycin administration, both systemic and local, using companion animals as models. We selected 22 canine patients which failed to achieve a complete response after an ECT treatment session. Eleven underwent another standard ECT session (control group), while 11 received a combined local and systemic administration of bleomycin in the second treatment session. Results According to the WHO criteria, the response rates in the combined administration group were: complete response (CR) 54% (6), partial response (PR) 36% (4), stable disease (SD) 10% (1). In the control group, these were: CR 0% (0), PR 19% (2), SD 63% (7), progressive disease (PD) 18% (2). In the combined group 91% objective responses (CR+PR) were obtained. In the control group 19% objective responses were obtained. The difference in the response rate between the treatment groups was significant (p < 0.01). Conclusions Combined local and systemic bleomycin administration was effective in previously to ECT non responding canine patients. The results indicate that this approach could be useful and effective in specific population of patients and reduce the number of treatment sessions needed to obtain an objective response.Abstract Background Electrochemotherapy (ECT), a medical treatment widely used in human patients for tumor treatment, increases bleomycin toxicity by 1000 fold in the treated area with an objective response rate of around 80%. Despite its high response rate, there are still 20% of cases in which the patients are not responding. This could be ascribed to the fact that bleomycin, when administered systemically, is not reaching the whole tumor mass properly because of the characteristics of tumor vascularization, in which case local administration could cover areas that are unreachable by systemic administration. Patients and methods We propose combined bleomycin administration, both systemic and local, using companion animals as models. We selected 22 canine patients which failed to achieve a complete response after an ECT treatment session. Eleven underwent another standard ECT session (control group), while 11 received a combined local and systemic administration of bleomycin in the second treatment session. Results According to the WHO criteria, the response rates in the combined administration group were: complete response (CR) 54% (6), partial response (PR) 36% (4), stable disease (SD) 10% (1). In the control group, these were: CR 0% (0), PR 19% (2), SD 63% (7), progressive disease (PD) 18% (2). In the combined group 91% objective responses (CR+PR) were obtained. In the control group 19% objective responses were obtained. The difference in the response rate between the treatment groups was significant (p < 0.01). Conclusions Combined local and systemic bleomycin administration was effective in previously to ECT non responding canine patients. The results indicate that this approach could be useful and effective in specific population of patients and reduce the number of treatment sessions needed to obtain an objective response.

Canine Oral Eosinophilic Granuloma Treated with Electrochemotherapy

A case of a canine oral eosinophilic granuloma in a 14-year-old female crossbred is described. The dog was presented with a history of ptyalism, halitosis, local pain, decreased appetite, and blood staining noted on food and water bowls. Clinical, hematologic, and biochemical examinations, abdominal ultrasonography, and 3-view chest radiographs were performed, and no metastases were found. Histopathologic examination of two 6 mm punch biopsies from the oral lesion revealed the presence of eosinophilic granulomatous lesions in the submucosa. After treatment with corticosteroids and wide spectrum antibiotics no significant changes in clinical signs and lesion size were observed. Electrochemotherapy (ECT), a novel tumor treatment routinely used for cutaneous and subcutaneous tumors in human patients in the European Union since 2006, was used to treat the eosinophilic granuloma. The procedure was performed under general anesthesia, followed by intravenous administration of bleomycin. Six weeks after treatment a complete response with disappearance of the mass and improvement of clinical signs were observed.

Minimally invasive electrochemotherapy procedure for treating nasal duct tumors in dogs using a single needle electrode

Abstract Background Nasal cavity tumors are usually diagnosed late, when they already have infiltrated adjacent tissues thus requiring very aggressive treatments with serious side effects. Here we use electrochemotherapy (ECT), a well demonstrated treatment modality for superficial tumors. Materials and methods In the case of deep-seated tumors, the main limitation of ECT is reaching the tumor with an appropriate electric field. To overcome this limitation we introduce the single needle electrode (SiNE), a minimally invasive device that can deliver an appropriate electric field with a simple procedure. Twenty-one canine patients with spontaneous tumors were selected, eleven were treated using the SiNE with ECT, and ten with surgery plus adjuvant chemotherapy as a control group. Results In the SiNE group, 27% achieved a complete response, 64% had a partial response, and 9% had a stable disease. This means that 91% of objective responses were obtained. The mean overall survival was 16.86 months (4–32 months, median 16.5 months), with a survival rate significantly higher (p = 0.0008) when compared with control group. The only side effect observed was the inflammation of the treated nasal passage, which was controlled with corticosteroid therapy for one week. One year after the treatment, 60% of the canine of the SiNE group vs. 10% of the control group remained alive, and after the 32 months follow-up, the survival rate were 30% and 0%, respectively. Conclusions ECT with the SiNE can be safely used in canine to treat nasal tumors with encouraging results.

Effects of Pulse Addition in Electropermeabilization: Theoretical Insights on the Electric Conductivity

The electrochemical treatment (ECT) of solid tumors is an electropermeabilization technique firmly established and widely used. In ECT protocols, pulse intensity as well as tissue electric conductivity are of utmost importance for assessing the final electropermeabilized area. Present ECT mathematical modeling based on the solution of the nonlinear Laplace equation for the electric field with a conductivity coefficient depending on the electric field and the temperature have greatly contributed to ECT protocol optimization. However, experimental results from literature report that a succession of pulses may increase tissue electric conductivity and the extent of tissue permeabilization, a phenomenon that present models fail to describe. Here we present new insights of a recently introduced ECT theoretical model that takes into account the effect of pulse addition on tissue electric conductivity. The model describes the electric field with the nonlinear Laplace equation with a conductivity coefficient depending on the electric field, the temperature and the quantity of pulses applied. ECT theoretical predictions show that the rise in the electric current density during the addition of pulses is due solely to an increment in the tissue electric conductivity with no significant changes in the electric field. A potential consequence of these results is that, under certain conditions, it would be possible to obtain larger electropermeabilized areas with the same pulse amplitude simply by increasing the number of pulses. The theoretical implications of this new model lead to a more realistic description of the EP phenomenon, hopefully providing more accurate predictions of ECT treatment outcomes.

Electrolytic Ablation Dose Planning Methodology

Electrolytic ablation (EA), a medical treatment increasingly used in solid tumor ablation, consists in the passage of a low direct electric current through two or more electrodes inserted in the tissue thus inducing pH fronts that destroys the tumor. The combined use of EA with a recently introduced one-probe two electrode device (OPTED) results in a minimally invasive tissue ablation technique. Despite its success related to low cost and minimum side effects, EA has drawbacks such as the difficulty in determining the current and time needed to assure total tumor ablation while avoiding healthy tissue intrusion. Here we introduce a realistic dose planning methodology in terms of the coulomb dosage administered and the associated pH tracking, that predicts an optimal EA/OPTED protocol treatment for a given tumor size, that is, the current and exposition time necessary to succeed in eliminating all the tumor mass while minimizing healthy tissue damage.

Amelanotic melanoma of the root of the tongue in a canine patient treated by electrochemotherapy

Background: Electrochemotherapy is a novel tumor treatment routinely used for cutaneous and subcutaneous tumors in human patients in the European Union since 2006. Here we used it to treat an amelanotic melanoma of the root of the tongue in a canine patient. Case Presentation: The patient was a 9 year-old, female, Golden Retriever, dehydrated, cachectic and in a bad general condition due to the difficulty in eating and drinking provoked by the tumor. The procedure was performed with general anesthesia, with intravenous administration of bleomycin, and went uneventful. The only adverse effect was an important swelling of the tongue which lasted 2 days and was controlled with non-steroidal anti-inflammatory drugs. Results and Conclusion: A good local control of the disease was achieved with a 83% reduction of the tumor mass, at day 21 after a single treatment. On the 33 rd day the patient died after a digestive hemorrhage not related to the treatment. Electrochemotherapy was found a good approach to locally control the disease. The swelling of the tongue was an important side effect which has to be taken into account when treating this organ, and should be controlled with medication.