Nanosecond pulsed electric fields stimulate apoptosis without release of pro-apoptotic factors from mitochondria in B16f10 melanoma

Nanosecond pulsed electric fields (nsPEFs) eliminates B16f10 melanoma in mice, but cell death mechanisms and kinetics of molecular events of cell death are not fully characterized. Treatment of B16f10 cells in vitro resulted in coordinate increases in active caspases with YO-PRO-1 uptake, calcium mobilization, decreases in mitochondria membrane potential with decreases in forward light scatter (cell size), increases in ADP/ATP ratio, degradation of actin cytoskeleton and membrane blebbing. However, there was no mitochondrial release of cytochrome c, AIF or Smac/DIABLO or generation of reactive oxygen species. Phosphatidylserine externalization was absent and propidium iodide uptake was delayed in small populations of cells. The results indicate that nsPEFs rapidly recruit apoptosis-like mechanisms through the plasma membrane, mimicking the extrinsic apoptosis pathway without mitochondrial amplification yet include activation of initiator and executioner caspases. nsPEFs provide a new cancer therapy that can bypass cancer-associated deregulation of mitochondria-mediated apoptosis in B16f10 melanoma.