Hypoxia and etanidazole alter radiation-induced apoptosis in HL60 cells but not in MOLT-4 cells

Int J Radiat Biol. 2002 Apr;78(4):267-74. doi: 10.1080/09553000110105695.


Purpose: To examine how hypoxia influences ionizing irradiation-induced apoptosis in cultured mammalian cells and how a hypoxic cell radiosensitizer sensitizes apoptosis under hypoxic conditions.

Materials and methods: Two cell lines derived from human lymphocytes, HL60 and MOLT-4, were exposed to 15 Gy X-rays under aerobic and hypoxic conditions. Etanidazole was used as a hypoxic cell radiosensitizer. The apoptotic morphological changes of nuclei and the induction of ladder-like DNA fragmentation were assessed by fluorescence microscopy and agarose gel electrophoresis, respectively.

Results: In HL60 cells, apototic cell death and the activation of caspases 8, 9 and 3 were less induced under the hypoxic conditions than under the aerobic ones. Treatment of hypoxic cells with etanidazole enhanced X-ray-induced apoptosis and caspase activation. However, in MOLT-4 cells, neither hypoxia nor etanidazole influenced X-ray-induced apoptosis and caspase activation. In both cell lines, the frequency of X-ray-induced DNA double-strand breaks (DSB) under hypoxia was significantly smaller than that in aerobic conditions. Treatment of hypoxic cells with etanidazole enhanced them.

Conclusion: These results suggested that X-ray-induced apoptosis in HL60 cells was initiated by DNA DSB and the treatment of hypoxic cells with etanidazole sensitized them through the enhancement of DSB induction, whereas X-ray-induced apoptosis in MOLT-4 cells occurred through damage other than to DNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoptosis / drug effects*
  • Apoptosis / radiation effects*
  • Bromodeoxyuridine / pharmacology
  • Caspases / metabolism
  • Cell Hypoxia / physiology*
  • Cell Line
  • DNA Damage
  • Enzyme Activation / drug effects
  • Enzyme Activation / radiation effects
  • Etanidazole / pharmacology*
  • HL-60 Cells
  • Humans
  • Radiation Tolerance / drug effects
  • Radiation-Sensitizing Agents / pharmacology*


  • Radiation-Sensitizing Agents
  • Etanidazole
  • Caspases
  • Bromodeoxyuridine