Biomedical subjects

D Miklavcic

Publications and source records attributed to D Miklavcic.

At least 37 records · Page 2Linked to original sources

PubMed2000

Electrochemotherapy with cisplatin: clinical experience in malignant melanoma patients.

Electrochemotherapy consists of chemotherapy followed by local application of electric pulses to the tumor to increase drug delivery into the cells. The aim of this Phase II clinical study was to evaluate the antitumor effectiveness of electrochemotherapy using intratumoral cisplatin administration on cutaneous tumor nodules in malignant melanoma patients. In 10 patients, 133 tumor nodules of different sizes were treated: (a) 82 tumor nodules were treated with electrochemotherapy; (b) 27 tumor nodules were treated with cisplatin; (c) 2 tumor nodules were treated with electric pulses; and (d) 22 tumor nodules were untreated. Four weeks after therapy, 78% objective responses were obtained in the electrochemotherapy group, and 38% objective responses were obtained in the cisplatin group. Exposure of tumor nodules to electric pulses without cisplatin treatment had no effect on tumor growth. Electrochemotherapy was well tolerated by all patients, and a good cosmetic effect was obtained, with only minimal scarring and a slight depigmentation of the skin. At 124 weeks of follow-up, a 77% control rate of the tumor nodules treated by electrochemotherapy was observed, compared to 19% for those that were treated with cisplatin only (P < 0.0001). Our results clearly demonstrate that electrochemotherapy with cisplatin is a highly effective approach for treatment of cutaneous malignant melanoma nodules. The advantages of this therapy include its simplicity, the short duration of treatment sessions, low cisplatin doses, and insignificant side effects, as well as the fact that it can be done on an outpatient basis.

Adult↗

PubMed2000

Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields.

The paper deals with the power dissipation caused by exposure of biological cells to electric fields of various frequencies. With DC and sub-MHz AC frequencies, power dissipation in the cell membrane is of the same order of magnitude as in the external medium. At MHz and GHz frequencies, dielectric relaxation leads to dielectric power dissipation gradually increasing with frequency, and total power dissipation within the membrane rises significantly. Since such local increase can lead to considerable biochemical and biophysical changes within the membrane, especially at higher frequencies, the bulk treatment does not provide a complete picture of effects of an exposure. In this paper, we theoretically analyze the distribution of power dissipation as a function of field frequency. We first discuss conductive power dissipation generated by DC exposures. Then, we focus on AC fields; starting with the established first-order model, which includes only conductive power dissipation and is valid at sub-MHz frequencies, we enhance it in two steps. We first introduce the capacitive properties of the cytoplasm and the external medium to obtain a second-order model, which still includes only conductive power dissipation. Then we enhance this model further by accounting for dielectric relaxation effects, thereby introducing dielectric power dissipation. The calculations show that due to the latter component, in the MHz range the power dissipation within the membrane significantly exceeds the value in the external medium, while in the lower GHz range this effect is even more pronounced. This implies that even in exposures that do not cause a significant temperature rise at the macroscopic, whole-system level, the locally increased power dissipation in cell membranes could lead to various effects at the microscopic, single-cell level.

Animals↗

PubMed1999

Blood perfusion of subcutaneous tumours in mice following the application of low-level direct electric current.

Electrotherapy with low-level direct electric current has been proved to be an effective local treatment of solid tumours. In the presented study an attempt was made to evaluate the effect of a single treatment with electrotherapy on blood perfusion of solid subcutaneous fibrosarcoma Sa-1 tumours in A/J mice. The tissue-staining method with Patent blue-violet dye, the rubidium extraction technique, and the noninvasive near-infrared spectroscopy method were used for this purpose. Results of all methods indicate that perfusion and subsequently oxygenation of tumours were reduced due to application of electrotherapy.

Animals↗

PubMed1999

Increased platinum accumulation in SA-1 tumour cells after in vivo electrochemotherapy with cisplatin.

Electrochemotherapy is an anti-tumour treatment that utilizes locally delivered electric pulses to increase cytotoxicity of chemotherapeutic drugs. The aim of our study was to determine whether anti-tumour effectiveness of electrochemotherapy with cisplatin is a consequence of increased plasma membrane permeability caused by electroporation that enables cisplatin binding to DNA. For this purpose, anti-tumour effectiveness of electrochemotherapy was evaluated on SA-1 tumours treated with electric pulses 3 min after intravenous injection of cisplatin (4 mg kg(-1)). Anti-tumour effectiveness was correlated with platinum accumulation in tumours and the amount of platinum bound to DNA, as determined by atomic absorption spectrometry. In tumours treated with electrochemotherapy, cell kill was increased by a factor of 20 compared with treatment with cisplatin only, as determined from tumour growth curves. The amount of platinum bound to DNA and platinum content in the tumours treated by electrochemotherapy was approximately two times higher than in cisplatin-treated tumours. Based on our results, we conclude that in vivo application of electric pulses potentiates anti-tumour effectiveness of cisplatin by electroporation that consequently results in cisplatin increased delivery into the cells. In addition, besides electroporation, immune system and tumour blood flow changes could be involved in the observed anti-tumour effectiveness of electrochemotherapy.

Animals↗

PubMed1998

The importance of electric field distribution for effective in vivo electroporation of tissues.

Cells exposed to short and intense electric pulses become permeable to a number of various ionic molecules. This phenomenon was termed electroporation or electropermeabilization and is widely used for in vitro drug delivery into the cells and gene transfection. Tissues can also be permeabilized. These new approaches based on electroporation are used for cancer treatment, i.e., electrochemotherapy, and in vivo gene transfection. In vivo electroporation is thus gaining even wider interest. However, electrode geometry and distribution were not yet adequately addressed. Most of the electrodes used so far were determined empirically. In our study we 1) designed two electrode sets that produce notably different distribution of electric field in tumor, 2) qualitatively evaluated current density distribution for both electrode sets by means of magnetic resonance current density imaging, 3) used three-dimensional finite element model to calculate values of electric field for both electrode sets, and 4) demonstrated the difference in electrochemotherapy effectiveness in mouse tumor model between the two electrode sets. The results of our study clearly demonstrate that numerical model is reliable and can be very useful in the additional search for electrodes that would make electrochemotherapy and in vivo electroporation in general more efficient. Our study also shows that better coverage of tumors with sufficiently high electric field is necessary for improved effectiveness of electrochemotherapy.

Animals↗

PubMed1998

Calculation of the electrical parameters in electrochemotherapy of solid tumours in mice.

Electrochemotherapy is a novel approach in chemotherapeutic drug delivery into tumours. Short intense direct current electric pulses are applied to tumour tissue causing electropermeabilisation thus enabling entrance of chemotherapeutic drugs into cells which otherwise do not easily penetrate. A three dimensional anatomically based finite element model of the mouse with injected subcutaneous solid tumour was built. The main goal of the study was to evaluate the influence of the electrode orientation on the distribution of electric field in the tumour and surrounding tissue during electrochemotherapy. Two electrode configurations, previously examined in experimental study, were modelled. Electric field distributions were calculated for each configuration. The main conclusion of our study is that changing electrode orientation strongly influences the distribution of the electric field inside the tumour in the electrochemotherapy of solid tumours in mice, which is in good agreement with the results of the experimental study. The efficacy of the electrochemotherapy depends on the magnitude of the electric field intensity inside tumour tissue.

Animals↗

PubMed1998

Electrochemotherapy with cisplatin: potentiation of local cisplatin antitumour effectiveness by application of electric pulses in cancer patients.

This study was aimed at assessing the response to electrochemotherapy with cisplatin of cutaneous tumour nodules in patients with malignant melanoma, squamous cell carcinoma and basal cell carcinoma. In 4 patients, 30 tumour nodules of different sizes were treated; five without treatment, one with electric pulses, five with cisplatin injected intratumorally and 19 with electrochemotherapy, i.e. intratumoral administration of cisplatin followed by delivery of electric pulses to the tumour nodule. After 4 weeks, a complete response (CR) in all 19 electrochemotherapy treated nodules was obtained. All electrochemotherapy treated nodules remained in CR (range 7-11 months), regardless of histological type, except for the metastasis of a squamous cell carcinoma that progressed after 9 months. CR was also obtained in two of five tumour nodules treated with cisplatin intratumorally, but the other three nodules progressed within 3-7 months. Exposure of the tumour nodule to electric pulses without cisplatin treatment had no effect on tumour growth. Electrochemotherapy was well tolerated by all patients and a good cosmetic effect was obtained, with only minimal scarring and a slight depigmentation of the skin. Electrochemotherapy with cisplatin has proved to be effective in patients with cutaneous tumour nodules. Furthermore, electrochemotherapy is easy to perform and can be carried out on an out-patient basis.

Antineoplastic Agents↗

PubMed1998

Effective treatment of cutaneous and subcutaneous malignant tumours by electrochemotherapy.

Electrochemotherapy (ECT) enhances the effectiveness of chemotherapeutic agents by administering the drug in combination with short intense electric pulses. ECT is effective because electric pulses permeabilize tumour cell membranes and allow non-permeant drugs, such as bleomycin, to enter the cells. The aim of this study was to demonstrate the anti-tumour effectiveness of ECT with bleomycin on cutaneous and subcutaneous tumours. This article summarizes results obtained in independent clinical trials performed by five cancer centres. A total of 291 cutaneous or subcutaneous tumours of basal cell carcinoma (32), malignant melanoma (142), adenocarcinoma (30) and head and neck squamous cell carcinoma (87) were treated in 50 patients. Short and intense electric pulses were applied to tumours percutaneously after intravenous or intratumour administration of bleomycin. The tumours were measured and the response to the treatment evaluated 30 days after the treatment. Objective responses were obtained in 233 (85.3%) of the 273 evaluable tumours that were treated with ECT. Clinical complete responses were achieved in 154 (56.4%) tumours, and partial responses were observed in 79 (28.9%) tumours. The application of electric pulses to the patients was safe and well tolerated. An instantaneous contraction of the underlying muscles was noticed. Minimal adverse side-effects were observed. ECT was shown to be an effective local treatment. ECT was effective regardless of the histological type of the tumour. Therefore, ECT offers an approach to the treatment of cutaneous and subcutaneous tumours in patients with minimal adverse side-effects and with a high response rate.

Adenocarcinoma↗

PubMed1998

Intratumoral cisplatin administration in electrochemotherapy: antitumor effectiveness, sequence dependence and platinum content.

Electrochemotherapy using intratumoral cisplatin administration was tested on EAT tumors in mice. Mice were treated with eight electric pulses (100 micros, 1 Hz, 1040 V) and/or cisplatin (1, 2, 4 and 8 mg/kg). Cisplatin treatment resulted in up to 20 days of tumor growth delay. Electrochemotherapy resulted in tumor cures; local tumor control reached a plateau at 4 mg/kg in 67% of tumor cures. The maximal effect of electrochemotherapy was achieved when cisplatin was injected 5 min before or simultaneously with electric pulses application. Approximately two times more platinum was bound to DNA in electrochemotherapy than in cisplatin treated tumors at all time points tested. Our study shows that electrochemotherapy with intratumoral cisplatin administration is a very effective local treatment of EAT tumors with high curability rate.

Animals↗

PubMed1998

Intrinsic sensitivity of tumor cells to bleomycin as an indicator of tumor response to electrochemotherapy.

Electrochemotherapy (ECT) involves the use of locally applied electric pulses to increase delivery of chemotherapeutic drugs into cells in tissues. ECT with bleomycin (BLM) is a very effective local treatment, but different tumors have different response rates to ECT. The aim of our study was to compare the responsiveness of SA-1 and EAT tumors to BLM and ECT in vitro and in vivo, in order to find possible reasons for the observed difference in response rate. The difference in sensitivity to ECT in vitro between the SA-1 and EAT cells was 10-fold and was the same as the difference in sensitivity to chronic BLM exposure, as measured by tetrazolium-based colorimetric (MTT) assay. This difference in sensitivity between SA-1 and EAT to ECT was also reflected in tumor cure rate. A six-times lower dose of BLM was needed to obtain local tumor control in SA-1 than in EAT tumors. Therefore, we suggest that the difference in sensitivity to BLM and ECT predominantly reflects the difference in intrinsic sensitivity of the cells to BLM.

Animals↗

PubMed1997

Anti-tumor effectiveness of electrochemotherapy with bleomycin is increased by TNF-alpha on SA-1 tumors in mice.

With the aim to increase anti-tumor effectiveness of electrochemotherapy, adjuvant immunotherapy with tumor necrosis factor-alpha (TNF-alpha) was tested on tumors in mice. Increased anti-tumor effectiveness on SA-1 tumors was observed after combining TNF-alpha, injected either intratumorally or peritumorally, with electrochemotherapy using suboptimal dose of bleomycin (BLM). The increased anti-tumor effectiveness was neither the result of potentiated anti-tumor effectiveness of TNF-alpha due to exposure of tumors to electric pulses, nor due to interaction with BLM. Therefore, the effect of adjuvant TNF-alpha treatment might be immunomodulatory, augmenting the anti-tumor activity of electrochemotherapy, and possibly adding a systemic component to the localized electrochemotherapy treatment.

Animals↗

PubMed1997

Electric current density imaging of mice tumors.

The use of electric current density imaging (CDI) to map spatial distribution of electric currents through tumors is presented. Specifically, a method previously tested on phantoms was implemented in vivo and in vitro for mapping electric current pulses of the same order of magnitude (j approximately 2500 A/m2) as in electrochemotherapy through T50/80 mammary carcinomas, B-16 melanomas and SA-1 sarcomas. A technically simplified method of electric current density imaging is discussed as well. Three geometries of electrodes (flat-flat, point-point, point-flat) indicate altered electric current distribution for the same tumor. This indicates that the method can be used for monitoring the effects of electrochemotherapy as a function of electrode geometry.

Animals↗

PubMed1997

Host's immune response in electrotherapy of murine tumors by direct current.

Electrotherapy by low level direct current has been demonstrated to have antitumor effects in different murine tumor models and in clinics. Electrotherapy in "field" configuration, where electrodes are placed subcutaneously outside of the tumor in a way that tumor lies in between the electrodes, was performed in immunodeficient nude and immunocompetent mice. Electrotherapy was much more effective in immunocompetent mice based on the observed tumor growth retardation, thus demonstrating that antitumor effectiveness of electrotherapy greatly depends on host's immune response. Further experiments were conducted by combining electrotherapy with concomitant immunotherapy in order to potentiate the antitumor effect of electrotherapy. Immunotherapy consisted of local delivery of genetically engineered cells selected for IL-2 secretion. This combined treatment was much more effective than any of the treatments alone.

Animals↗

PubMed1996

Electrochemotherapy with bleomycin in SA-1 tumor-bearing mice--natural resistance and immune responsiveness.

Electrochemotherapy is an antitumor treatment that utilizes locally delivered electric pulses to increase the effectiveness of chemotherapeutic drugs in cells and tissues. Electric pulses permeabilize tumor cells to allow nonpermeant drugs such as bleomycin to enter the cells. Although preclinical data indicate that immune responsiveness of the organism is important for obtaining cures of the tumors after electrochemotherapy with bleomycin, it is not known how electrochemotherapy affects the immune system of the organism. The aim of the study was to determine the effects of electrochemotherapy with bleomycin on natural resistance and immune responsiveness. Natural resistance was evaluated by phagocytic and intracellular killing activity (oxidative burst) in monocytes and polymorphonuclear granulocytes from venous blood, and immune responsiveness by blast transformation of spleen mononuclear cells to mitogens. The percentage of monocytes in venous blood able to elicit oxidative burst was significantly increased 7 days after the electrochemotherapy and returned to normal values after 14 days. In addition, increased blast transformation of spleen mononuclear cells by stimulation with concanavalin A (T lymphocytes activity) was found 14 days after electrochemotherapy treatment. The results of our study demonstrate that electrochemotherapy with bleomycin affects the immune system of the organism

Animals↗

PubMed1995

Antitumor effectiveness of electrochemotherapy with cis-diamminedichloroplatinum(II) in mice.

One of the ways to increase drug delivery into cells and tissues is by a local application of short, intense electric pulses, i.e., electropermeabilization. This approach is used in electrochemotherapy to potentiate antitumor effectiveness of chemotherapeutic drugs. To determine whether electropermeabilization can potentiate antitumor effectiveness of cis-diamminedichloroplatinum(II) (CDDP), electrochemotherapy with CDDP was tested in vitro and in vivo on s.c. SA-1, EAT, and melanoma B16 tumors in mice. Electric pulses were applied to the tumors by percutaneously placed electrodes after i.v. injection of CDDP. Severalfold potentiation of CDDP antitumor effectiveness with electric pulses was obtained, inducing partial or complete responses in tumor growth. Electrochemotherapy was CDDP dose dependent, as well as dependent upon the amplitude of electric pulses. Also important was the sequencing and the interval of CDDP administration, relative to application of electric pulses. Specifically, a good antitumor effect without side effects was obtained with eight electric pulses (electric pulse amplitude, 1040 V; repetition frequency, 1 Hz; pulse width, 100 microseconds; electrode distance, 8 mm; 1300 V/cm) applied 3 min after i.v. injection of 4 mg/kg CDDP. With a higher CDDP dose (8 mg/kg), some long-term complete responses were obtained (14%) on melanoma B16 tumors. Thus, electrochemotherapy with CDDP offers an approach to making chemotherapy with CDDP more effective.

Animals↗

PubMed1994

Anti-tumor effect of tumor necrosis factor combined with electrotherapy on mouse sarcoma.

Anti-tumor effectiveness of tumor necrosis factor (TNF)-alpha applied peritumorally was assessed in combination with local electrotherapy on subcutaneous SA-1 tumors in mice. TNF and electrotherapy each induced significant tumor growth delay. In combined treatment using TNF and electrotherapy, a synergistic anti-tumor effect was observed, regardless of whether TNF was injected before or after electrotherapy. An extra anti-tumor effect was achieved when TNF in the same total dose (2 x 10(5) U) was split into a priming dose (0.5 x 10(5) U) 1 h before electrotherapy and the other (1.5 x 10(5) U) 24 h thereafter. As the result of this therapeutic combination survival rate of the animals was 40%. No animal survived more than 50 days in groups subjected to TNF or electrotherapy treatment alone. Combined treatment with TNF and electrotherapy induced massive tumor destruction, confirmed by histological examination 2 days after the treatment. The results indicate that TNF and electrotherapy interact and that they can be effective in control of local tumor growth.

Animals↗

PubMed1993

Potentiation of bleomycin antitumor effectiveness by electrotherapy.

Electrotherapy was investigated for its ability to increase the responsiveness of murine tumors to bleomycin treatment. Mice bearing fibrosarcoma were treated with 250 micrograms bleomycin and then with 0.6 mA direct current (DC) for 60 min. Antitumor effects of single treatments were moderate with bleomycin, but significant with electrotherapy. Combined treatment with bleomycin followed by electrotherapy was more effective than either treatment alone. Tumor growth delay of the animals after combined treatment was greater than the summation of tumor growth delays after single treatments. The results of our study indicate that bleomycin and electrotherapy treatments interact, with electrotherapy potentiating the effectiveness of bleomycin treatment.

Animals↗

PubMed1992

Modified cell proliferation due to electrical currents.

In view of the evidence that electrical currents may enhance healing of chronic wounds and retard tumour growth it is suggested that these currents normalise cell proliferation. Additional support to this contention is given by two reports: one on healing of pressure sores in man and one on tumour growth retardation in mice. The effect of an ionic environment on the cell cycle is analysed. Finally a hypothesis attempting to explain the normalising effect of electrical currents on cell proliferation is proposed. It is known that non-dividing cells, e.g. mature neurons, have high transmembrane potential (TMP) whereas fast-dividing cells, e.g. cancerous cells, have low TMP. When a cell is exposed to an electrical field, one side of the cell becomes hyperpolarised while the opposite side is depolarised. Assuming a nonlinear relationship between TMP and the transmembrane ionic currents, it can be shown that in non-dividing cells their high TMP is lowered; whereas in cells with a high division rate, their low TMP is raised due to cell exposure to the external electrical field. These alterations in transmembrane potential could contribute to the normalisation of abnormal cell proliferation.

Animals↗