Increased cell killing and DNA damage in cells exposed to ultra-short pulsed electric fields

We investigated the effects of nanosecond pulsed electric fields (nsPEF) on DNA structure and on survival of two human leukemia cell lines (Jurkat and HL60) in vitro. DNA damage was evaluated using single cell gel electrophoresis methods (comet assay) and sensitivity of cells to nsPEF determined by clonogenic cell survival. nsPEF applications using pulse durations of 10, 60 or 300 nanosecond duration with voltage amplitudes of 300, 60 and 60kv/cm respectively were applied to cells in trains of 1, 5, or 10 pulses. Jurkat and HL60 cells both showed DNA damage following exposure to different nsPEF parameters. Comet length increased in Jurkat cells by 22.5% at one, 33.2% at five and 62% at ten 60ns pulses compared to non-exposed cells. HL60 showed increases in comet length of 28.6%. 23.5% and 41.2% after one pulse of 10, 60 and 300ns duration, respectively. Cell survival curves for both cell types showed a decrease (90+/-4%) in cell survival following one 60 or 300ns pulse. A further dramatic decrease in cell survival was not observed following 5 and 10 pulses. These data show that exposure to nsPEF applications induces DNA damage and decreases cell survival in vitro.