Membrane electroporation increases photodynamic effects

Electroporation of membranes is used widely for drug delivery. Photodynamic action consists of three main steps: (A) incorporation of the sensitizer through a membrane into cells; (B) photoxidation of cell constituents and (C) reoxidation of the reduced sensitizer by oxygen etc. The mechanisms of (B) and (C) have been studied widely in past decades. However, the mechanism of transport (A) of sensitizers to targets as the rate limiting step has not been studied to the same extent. Therefore we applied membrane and cell wall electroporation of human histiocytic lymphoma U937 and Saccharomyces cerevisiae cells in order to incorporate rapidly the reliable photodynamic agents thiopyronine, protoporphyrin, zinc phthalocyanine, copper phthalocyanine sulfonate, adriamycin and daunomysin, well-tried cytostatic agents. Depending on field strength and pulse width, 50-90% of cells become electroporated, then the dye diffuses rapidly into the cells, which reseal their membranes over a period of 6-10 min. Illumination for 10-15 min destroys all resealed cells faster than the same amount of unporated cells as in the case of the control (without pulse treatment) either by oxidation of cell components caused by excited dyes or singlet oxygen treatment. By this synergism of electroporation and photodynamic action at the same time, it is possible to kill all cells in a much shorter time than under usual conditions, e.g. in the control suspension. A combination of electrochemotherapeutic needle electrodes with a light conductor for a LASER connection will be effective for therapy.