Effective treatment of cutaneous and subcutaneous malignant tumours by electrochemotherapy LM Mir', LF Glass23, G Sersa4, J Teissi65, C Domenge6, D Miklavdid7, MJ Jaroszeski38, S Orlowski9, DS Reintgen38, Z Rudolf4, M Belehradek6, R Gilbertl0, M-P Rols5, J Belehradek Jr', JM Bachaud", R DeConti23, B Stabuc4, M Cemazar4, P Coninx'2 and R Heller38 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.

Transient membrane permeabilization by application of high electric field intensity pulses on cells (electropermeabilization) depends on several physical parameters associated with the technique (pulse intensity, number, and duration). In the present study, electropermeabilization is studied in terms of flow of diffusing molecules between cells and external medium. Direct quantification of the phenomenon shows that electric field intensity is a critical parameter in the induction of permeabilization. Electric field intensity must be higher than a critical threshold to make the membrane permeable. This critical threshold depends on the cell size. Extent of permeabilization (i.e., the flow rate across the membrane) is then controlled by both pulse number and duration. Increasing electric field intensity above the critical threshold needed for permeabilization results in an increase membrane area able to be permeabilized but not due to an increase in the specific permeability of the field alterated area. The electroinduced permeabilization is transient and disappears progressively after the application of the electric field pulses. Its life time is under the control of the electric field parameters. The rate constant of the annealing phase is shown to be dependent on both pulse duration and number, but is independent of electric field intensity which creates the permeabilization. The phenomenon is described in terms of membrane organization transition between the natural impermeable state and the electro-induced permeable state, phenomenon only locally induced for electric field intensities above a critical threshold and expanding in relation to both pulse number and duration.

Electrochemotherapy is a new anticancer therapy in which transient permeabilization of cells by an electric field induces a significant increase in the bleomycin concentration and toxicity in tumour cells. We report a clinical study of electrochemotherapy in malignant melanoma. The main issues addressed were the effect of the size of the nodules, the optimization of the electrical parameters, and posttreatment clinical observations. Four patients were enrolled in the study. They received a 10 mg/m2 dose of bleomycin administered intravenously, followed by short, intense electric pulses applied directly to the skin at the tumour sites. Antitumour effects were obtained, especially in the smallest nodules. Objective responses were obtained in more than 90% of the 55 nodules treated, with a complete response rate of 9%. All patients tolerated the treatment well. No residual effects from the electric pulses were observed, even when a high number of pulses were required or when two consecutive treatments were applied. These results are encouraging and the study should be continued.

Cells can be made temporarily permeable if pulsed by high-intensity short-duration electric fields. The molecular mechanisms underlying this electropermeabilization are still unknown. The kinetic events may be described by four successive steps: induction, expansion, stabilization, and resealing. On one hand, cell electropermeabilization is detected only under more stringent conditions when cells have been treated by ethanol. On the other hand, lysolecithin is observed to facilitate cell electropermeabilization. More precisely, these molecules that modify membrane order, when used in concentrations compatible with cell viability, are shown to affect only the expansion and resealing steps. Electropermeabilization is inducing a transition in the membrane organization. Membrane order is modulating the energy barrier needed to evoke this membrane transition which occurs when cells are submitted to a field larger than a characteristic threshold (expansion step). Less order would increase the magnitude of this energy barrier; more order would decrease it.

Swiss mouse 3T3-C2 fibroblasts, grown to confluence in monolayer culture, are shown to fuse when exposed to electric fields. Exposure to five repetitive electric pulses of about 1 kilovolt per centimeter with a duration of 50 microseconds caused approximately 20 percent of the cells to become fused (multinucleate) when 1 millimolar magnesium was present in the medium. The effects of minimum thresholds of field strength, pulse duration, and number of pulses were determined. Cell disruption was observed when the electric field exceeded 2.0 kilovolts per centimeter or the pulse was of longer duration than 120 microseconds.