Assessment of electroporation by flow cytometry

Background: Electroporation accomplishes transient permeabilization of cell s and thus aids in the uptake of drugs. The method has been employed clinic ally in the treatment of dermatological tumors with bleomycin. The conditio ns of electroporation are still largely empirical and information is lackin g as to the interrelationships among voltage pulse height, pulse number and toxicity, cell permeation, drug uptake, and effects on drug toxicity. We u sed propidium iodide CPD and flow cytometry to define cell permeation into cytoplasmic and nuclear compartments to determine the improvements of drug toxicity that can be accomplished by electroporation. Methods: Human squamous carcinoma cells of defined TP53 status and normal h uman epithelial cells were subjected to electroporation using a square wave pulse generator in the range of 0-5,000 V/cm. Flow cytometry served to est ablish entry; of the drug reporter, PI, into the cytoplasm and nucleus. A d ye staining method served to establish cell survival and to determine the t oxicity of bleomycin alone, electroporation alone, and electroporation with bleomycin. Results: The electric field intensity (EFI) required to produce 50% permeab ilization (EP50) is cell type dependent. The EP50 varied from 1,465 to 2,02 7 V/cm. An EFI below 900 V/cm is growth stimulatory whereas an EFI in exces s of 1,000 V/cm is growth inhibitory. An EFI of 1,000 V/cm is sufficient to increase bleomycin toxicity by a factor of 2-3. A differential electropora tion efficiency is observed between normal and tumor cells. Conclusions: Tumor cells can be targeted preferentially at electroporation voltages where normal cells are less permeable. Cytometry 41:96-101, 2000. (C) 2000 Wiley-Liss, Inc.