title: Dose-dependent ATP depletion and cancer cell death following calcium electroporation, relative effect of calcium concentration and electric field strength.
abstract: BACKGROUND
  Electroporation, a method for increasing the permeability of membranes to ions and small molecules, is used in the clinic with chemotherapeutic drugs for cancer treatment (electrochemotherapy). Electroporation with calcium causes ATP (adenosine triphosphate) depletion and cancer cell death and could be a novel cancer treatment. This study aims at understanding the relationship between applied electric field, calcium concentration, ATP depletion and efficacy.
  
  
  METHODS
  In three human cell lines--H69 (small-cell lung cancer), SW780 (bladder cancer), and U937 (leukaemia), viability was determined after treatment with 1, 3, or 5 mM calcium and eight 99 μs pulses with 0.8, 1.0, 1.2, 1.4 or 1.6 kV/cm. Fitting analysis was applied to quantify the cell-killing efficacy in presence of calcium. Post-treatment intracellular ATP was measured in H69 and SW780 cells. Post-treatment intracellular ATP was observed with fluorescence confocal microscopy of quinacrine-labelled U937 cells.
  
  
  RESULTS
  Both H69 and SW780 cells showed dose-dependent (calcium concentration and electric field) decrease in intracellular ATP (p<0.05) and reduced viability. The 50% effective cell kill was found at 3.71 kV/cm (H69) and 3.28 kV/cm (SW780), reduced to 1.40 and 1.15 kV/cm (respectively) with 1 mM calcium (lower EC50 for higher calcium concentrations). Quinacrine fluorescence intensity of calcium-electroporated U937 cells was one third lower than in controls (p<0.0001).
  
  
  CONCLUSIONS
  Calcium electroporation dose-dependently reduced cell survival and intracellular ATP. Increasing extracellular calcium allows the use of a lower electric field.
  
  
  CONCLUSIONS
  This study supports the use of calcium electroporation for treatment of cancer and possibly lowering the applied electric field in future trials.
authors: Center for Experimental Drug and Gene Electrotransfer, Department of Oncology, Copenhagen University Hospital Herlev, Copenhagen, Denmark.
authors: Emilie Louise
authors: EL
authors: Hansen
authors: Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, Virginia, United States of America.
authors: Esin Bengisu
authors: EB
authors: Sozer
authors: Institute for Electromagnetic Sensing of the Environment (IREA), Italian National Research Council, Naples, Italy.
authors: Stefania
authors: S
authors: Romeo
authors: Center for Experimental Drug and Gene Electrotransfer, Department of Oncology, Copenhagen University Hospital Herlev, Copenhagen, Denmark.
authors: Stine Krog
authors: SK
authors: Frandsen
authors: Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, Virginia, United States of America.
authors: P Thomas
authors: PT
authors: Vernier
authors: Center for Experimental Drug and Gene Electrotransfer, Department of Oncology, Copenhagen University Hospital Herlev, Copenhagen, Denmark.
authors: Julie
authors: J
authors: Gehl
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000008:administration & dosage*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D018274:Electroporation; D006801:Humans; D051379:Mice; D009369:Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology
chemical_list: D000255:Adenosine Triphosphate; D002118:Calcium