Fundamentals of electroporative delivery of drugs and genes

Electrooptical and conductometrical relaxation methods have given a new ins ight in the molecular mechanisms of the electroporative delivery of drug-li ke dyes and genes (DNA) to cells and tissues. Key findings are: (1) Membran e electroporation (ME) and hence the electroporative transmembrane transpor t of macromolecules are facilitated by a higher curvature of the membrane a s well as by a gradient of the ionic strength across charged membranes, aff ecting the spontaneous curvature. (2) The degree of pore formation as the p rimary field response increases continuously without a threshold field stre ngth, whereas secondary phenomena, such as a dramatic increase in the membr ane permeability to drug-like dyes and DNA (also called electropermeabiliza tion), indicate threshold field strength ranges. (3) The transfer of DNA by ME requires surface adsorption and surface insertion of the permeant molec ule or part of it. The diffusion coefficient for the translocation of DNA ( M-r approximate to 3.5 x 10(6)) through the electroporated membrane is D-m = 6.7 x 10(-13) cm(2) s(-1) and D-m for the drug-like dye Serva Blue G (M-r approximate to 854) is D-m = 2.0 x 10(-12) cm(2) s(-1). The slow electropo rative transport of both DNA and drugs across the electroporated membrane r eflects highly interactive (electro-) diffusion, involving many small pores coalesced into large, but transiently occluded pores (DNA). The data on mo use B-cells and yeast cells provide directly the flow and permeability coef ficients of Serva blue G and plasmid DNA at different electroporation proto cols. The physico-chemical theory of ME and electroporative transport in te rms of time-dependent flow coefficients has been developed to such a degree that analytical expressions are available to handle curvature and ionic st rength effects on ME and transport. The theory presents further useful tool s for the optimization of the ME techniques in biotechnology and medicine, in particular in the new field of electroporative delivery of drugs (electr ochemotherapy) and of DNA transfer and gene therapy. (C) 1999 Elsevier Scie nce S.A. All rights reserved.