Hoechst 33342 induces radiosensitization in malignant glioma cells via increase in mitochondrial reactive oxygen species

Abstract

Mitochondrial DNA plays an important role in cellular sensitivity to cancer therapeutic agents. Hoechst 33342, a DNA minor groove binding ligand, has shown radiosensitizing effects in different cancer cell lines. In the present study, the possible binding of Hoechst 33342 with mitochondrial DNA, isolated from human cerebral glioma (BMG-1) cells, was investigated and consequences of this binding on excessive reactive oxygen species (ROS) generation in irradiated BMG-1 cells were studied. Alteration in the fluorescence spectroscopic characteristics of Hoechst 33342 suggested binding of Hoechst 33342 with isolated mitochondria and mitochondrial DNA. Persistent increase in level of ROS in the presence of Hoechst 33342 has been observed, which was further enhanced in irradiated cells. Investigations using inhibitors of ETC complex I suggested that mitochondrial bound Hoechst 33342 contributed to increased ROS, which was associated with alteration in ΔΨm and antioxidant machinery. These factors appeared to contribute in potentiating radiation-induced cell death in BMG-1 cells. The finding from these studies will be useful in designing better anti-cancer strategies.

Keywords::

• Hoechst 33342
• mtDNA
• reactive oxygen species
• radiosensitization

Acknowledgement

We are thankful to Dr R. P. Tripathi, Director, Institute of Nuclear Medicine and Allied Sciences for support and constant encouragement.

Declaration of interest: This work was carried out as part of a project (INM 301) supported by DRDO from the Ministry of Defense, Government of India. Mr Mohammad Athar is a recipient of ICMR fellowship. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

This paper was first published online on Early Online on 17 June 2010.