Assessment of DNA damage produced by ¹²⁵I‐triplex‐forming oligonucleotides in cells

Abstract

Purpose: Triplex‐forming oligodeoxyribonucleotides (TFOs) bind specifically to their target sequences by forming hydrogen bonds within the major groove of the target duplex. When labeled with Auger‐electron‐emitting radioisotopes, TFOs are able to damage the target gene in a process named antigene radiotherapy. We compared radiotoxicity and the amount of DNA damage produced within cultured cells by two ¹²⁵I‐labeled TFOs, one with a single target in the genome and another with multiple targets.

Materials and methods: Radiotoxicity was measured by clonogenic assay while DNA damage was assessed by the number of histone γ‐H2AX foci formed at the sites of DNA double strand breaks (DSBs).

Results: The TFO with multiple nuclear targets was 1.7 fold more radiotoxic and produced on average 1.9 fold more γ‐H2AX foci per cell than the TFO with a single target.

Conclusion: Since the two methods gave comparable results, measuring the number of γ‐H2AX foci per decay may be a useful procedure for the assessment of cytotoxic effects and the intranuclear localization of radionuclides when they produce DSBs.