Importance of association between permeabilization and electrophoretic forces for intramuscular DNA electrotransfer

Gene transfer using electrical pulses is a rapidly expanding field. Many st udies have been performed in vitro to elucidate the mechanism of DNA electr otransfer. In vivo, the use of efficient procedures for DNA electrotransfer in tissues is recent, and the question of the implied mechanisms is largel y open. We have evaluated the effects of various combinations of square wav e electric pulses of variable field strength and duration, on cell permeabi lization and on DNA transfection in the skeletal muscle in vivo. One high v oltage pulse of 800 V/cm, 0.1 ms duration (short high pulse) or a series of four low voltage pulses of 80 V/cm, 83 ms duration (long low pulses) sligh tly amplified transfection efficacy, while no significant permeabilization was detected using the Cr-51-EDTA uptake test. By contrast, the combination of one short high pulse followed by four long low pulses led to optimal ge ne transfer efficiency, while inducing muscle fibers permeabilization. Thes e results are consistent with additive effects of electropermeabilization a nd DNA electrophoresis on electrotransfer efficiency. Finally, the describe d new combination, as compared to the previously reported use of repeated i dentical pulses of intermediate voltage, leads to similar gene transfer eff iciency, while causing less permeabilization and thus being likely less del eterious. Thus, combination of pulses of various strengths and durations is a new procedure for skeletal muscle gene transfer that may represents a cl ear improvement in view of further clinical development. (C) 2000 Elsevier Science B.V. All rights reserved.