Stephen J. Beebe
Old Dominion University, USA
Stephen J Beebe received his PhD at the Medical College of Ohio, now The University of Toledo College of Medicine. He was as post-doctoral fellow in the Howard Hughes Medical Institute in the Department of Molecular Physiology and Biophysics at Vanderbilt University. He then was a Fulbright Scholar in Oslo Norway before serving as an Assistant and Associate Professor at the Eastern Virginia Medical School in Departments of Physiological Sciences. He is now a Professor in the Frank Reidy Research Center for Bioelectrics at Old Dominion University, Norfolk Virginia. He is the author of over 100 peer reviewed published manuscripts.
Pulse power using nanosecond pulsed electric fields (nsPEFs) induced cell death inN1-S1 hepatocellular carcinoma (HCC) and Jurkat cells. To induce cell death, nsPEFs disruptedthe mitochondria membrane potential (ΔΨm), which is independent of nanoporation and Ca2+-dependent, and induced an influx of calcium through nanopores in the plasma membrane.This follows the “two hit” hypothesis where Ca2+ overload and another pathological stimulus, dissipation of ΔΨm, must be present to cause loss of cell viability.Effects of nsPEFs on Jurkat cells with deficiencies in FADD or caspase-8 had no effects on cytochrome c release or cell death, indicating oncogenic mechanisms for apoptosis evasion through death receptor pathwaysare readily surmountable by nsPEFs.Using Jurkat cells with deficiencies in APAF-1, nsPEF-induced cell death was caspase-dependent at lower electric fields and caspase-independent at higher electric fields. Thus, nsPEFs induce multiple forms of intrinsic cell death.Unlike apoptosis induced by heat or genotoxic stress, overexpression of Bcl-xl (8-fold) in Jurkat cells had no effect on nsPEF-induced dissipation of ΔΨm or viability. Thus, nsPEFs can bypass cancer mechanisms that protect mitochondrial function.In vivonsPEFs ablated 90% of orthotopic HCC.Caspase-9 and caspase-3, but not caspase-8, were activated. For rats with N1-S1 HCC tumors that were eliminated, a challenge injection of the same HCC cells in the same or adjacent liver lobes failed to establish tumors, while age-matched naïve control rats readily grew tumors. These results suggest a host-mediated immune response after clearance of rat N1-S1 HCC with nsPEFs.