Identification of in vitro electropermeabilization equivalent pulse protocols

Exposure of cells to an external sufficiently strong electric field results in the formation of pores across the membrane. This phenomenon, termed electropermeabilization, permits the transport of poorly permeant molecules into cytosol. In clinical practice, cell membrane permeabilization for drug electrotransfer is achieved using the ESOPE pulse protocol (1000 V/cm, 8 pulses, 100 μs, 5 kHz). The aim of this study was to investigate several combinations of electric field amplitude and pulse number able to induce electropermeabilization as the one observed when the ESOPE protocol was applied. Decreasing electric field amplitudes (1000 to 300 V/cm) in combination with increasing number of pulses (8 to 320) were applied to in vitro MG63 cells. Propidium iodide and Calcein blue AM uptake were used to evaluate cell electropermeabilization and viability. Results showed that the threshold of local electric field needed to obtain electropermeabilization decreased exponentially with increasing the number of pulses delivered (r2 5 0.92, p<0.0001). The absorbed dose threshold was dependent on the number of pulses for each voltage applied (r2 5 0.96, p<0.0001). In conclusion, the possibility of applying an increased number of pulses rather than increasing the electric field amplitude to perform electropermeabilization, may become an important tool for electropermeabilization-related clinical applications.