DNA fragmentation and caspase-independent programmed cell death by modulated electrohyperthermia

Strahlenther Onkol. 2014 Sep;190(9):815-22. doi: 10.1007/s00066-014-0617-1. Epub 2014 Feb 22.


Background and purpose: The electric field and the concomitant heat (electrohyperthermia) can synergistically induce cell death in tumor tissue, due to elevated glycolysis, ion concentration, and permittivity in malignant compared with nonmalignant tissues. Here we studied the mechanism and time course of tumor destruction caused by electrohyperthermia.

Material and methods: Bilateral implants of HT29 colorectal cancer in the femoral regions of Balb/c (nu/nu) mice were treated with a single 30-min shot of modulated, 13.56-MHz, radiofrequency-generated electrohyperthermia (mEHT). Tumors at 0, 1, 4, 8, 14, 24, 48, and 72 h posttreatment were studied for morphology, DNA fragmentation, and cell death response-related protein expression using tissue microarrays, immunohistochemistry, Western immunoblots, and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays.

Results: Modulated EHT treatment induced significant tumor destruction in HT29 xenografts with a peak of a sevenfold increase compared with the untreated controls. The significant treatment-related elevation of DNA fragmentation--detected with TUNEL assay--and apoptotic bodies between 24 and 72 h posttreatment was proof of a programmed cell death response. This was associated with significant mitochondrial accumulation of bax and mitochondrial-to-cytoplasmic release of cytochrome c proteins between 8 and 14 h. Cleaved caspase-3 levels were low and mainly localized to inflammatory cells. The substantial cytoplasmic-to-nuclear translocation of apoptosis-inducing factor (AIF) and its 57-kDa activated fragment detected between 14 and 24 h after treatment indicated AIF as an effector for DNA fragmentation.

Conclusion: Modulated EHT treatment can induce programmed cell death-related tumor destruction in HT29 colorectal adenocarcinoma xenografts, which dominantly follows a caspase-independent subroutine.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenocarcinoma / pathology*
  • Animals
  • Apoptosis / genetics
  • Apoptosis / radiation effects*
  • Caspase 2 / genetics*
  • Colorectal Neoplasms / pathology*
  • Cytochromes c / genetics
  • DNA Fragmentation / radiation effects*
  • Gene Expression Regulation, Neoplastic / radiation effects
  • HT29 Cells
  • Heterografts
  • Humans
  • Hyperthermia, Induced / instrumentation*
  • In Situ Nick-End Labeling
  • Magnetic Field Therapy / instrumentation*
  • Mice
  • Mice, Inbred BALB C
  • Mice, Nude
  • Mitochondria / radiation effects
  • Neoplasm Transplantation
  • Rats
  • bcl-2-Associated X Protein / genetics


  • Bax protein, mouse
  • bcl-2-Associated X Protein
  • Cytochromes c
  • Caspase 2