Electroporation of subcutaneous mouse tumors by rectangular and trapezium high voltage pulses.

The artificial electrotransfer of bioactive agents such as drugs, peptides or therapeutical nucleic acids and oligonucleotides by membrane electroporation (MEP) into single cells and tissue cells requires knowledge of the optimum ranges of the voltage, pulse duration and frequency of the applied pulses. For clinical use, the classical electroporators appear to necessitate some tissue specific presetting of the pulse parameters at the high voltage generator, before the actual therapeutic pulsing is applied. The optimum pulse parameters may be derived from the kinetic normal mode analysis of the current relaxations due to a voltage step (rectangular pulse). Here, the novel method of trapezium test pulses is proposed to rapidly assess the current (I)/voltage (U) characteristics (IUC). The analysis yields practical values for the voltage U(app) between a given electrode distance and pulse duration t(E) of rectangular high voltage (HV) pulses, to be preset for an effective in vivo electroporation of mouse subcutaneous tumors, clamped between two planar plate electrodes of stainless steel. The IUC of the trapezium pulse compares well with the IUC of rectangular pulses of increasing amplitudes. The trapezium pulse phase (s) of constant voltage and 3 ms duration, following the rising ramp phase (r), yields a current relaxation which is similar to the current relaxation during a rectangular pulse of similar duration. The fit of the current relaxation of the trapezium phase (s) to an exponential function and the IUC can be used to estimate the maximum current at a given voltage. The IUC of the falling edge (phase f) of the trapezium pulse serves to estimate the minimum voltage for the exploration of the long-lived electroporation membrane states with consecutive low-voltage (LV) pulses of longer duration, to eventually enhance electrophoretic uptake of ionic substances, initiated by the preceding HV pulses.