Nanosecond electric pulses induce DNA breaks in cisplatin-sensitive and -resistant human ovarian cancer cells.

Human ovarian cancer cells COC1 and COC1/DDP (cisplatin-resistant subline) were exposed to 6 kV/cm nanosecond electric pulses (nsEP) with a pulse length of 8, 16 or 24 ns. The potential in a subcellular unit was calculated using a multilayer dielectric spherical model, and area under the voltage-time curves (AUC) integrated with a lower limit of 0.2V. Cell viability was determined, and double-stand and total DNA breaks detected with the neutral and alkaline comet assays. nsEP evoked a higher voltage and AUC in nucleoplasm, and the levels in COC1 cells was just above those in COC1/DDP cells. Comets only appeared in the alkaline assay demonstrating single-stand DNA break. Fewer DNA break (16.51% vs. 35.13% at 24 ns, p=0.0150) and more survival (22.42% vs. 13.19% at 24 ns, p=0.0015) occurred in COC1/DDP cells despite an equal electric energy and almost equal cell sizes. 24-ns EP led to higher rates of cell-death and comet. The comet rate correlated with cell-death fraction in either cell line (r=0.5701, p=0.0135; r=0.5110, p=0.0302). There was no a correlation between the tail length, tail moment or Olive tail moment and cell-death rate. The data showed that response of chemosensitive cells differed from that of chemoresistant cells and DNA damage contributed to percent of cell death.