DNA damage, micronucleus formation, and cell death from 125I decays in DNA

Area of Science:

• Radiobiology
• Molecular and Cellular Biology
• Genetics

Background:

• Iodine-125 (125I) decays are a source of low linear energy transfer (LET) radiation, causing DNA damage and cell death.
• The biological impact of 125I depends on the time between incorporation into DNA and measurement, influencing the type and proximity of emitted electrons.
• Understanding the relationship between DNA double-strand breaks (DSBs) and cell killing is crucial for radiation biology and cancer therapy.

Purpose of the Study:

• To investigate the effect of storage time after 125I incorporation on cell killing in Chinese Hamster Ovary (CHO) cells.
• To determine if exposure to HAT medium alters the cell-killing pattern induced by 125I.
• To correlate cell death with DNA double-strand break (DSB) induction/repair and chromosome damage.

Main Methods:

• CHO cells were pulse-labeled with 125I-iododeoxyuridine.
• Cells were harvested at 30 minutes or 5 hours post-labeling and stored at -196°C to accumulate 125I decays.
• Some cell groups were exposed to HAT medium; survival curves, DNA DSB induction/repair, and micronucleus formation were analyzed.

Main Results:

• Cells harvested 30 minutes post-labeling showed low-LET survival curves, while 5-hour groups exhibited high-LET patterns.
• Exposure to HAT medium abolished this time-dependent shift, with both 30-minute and 5-hour groups displaying high-LET-type killing.
• Cell killing differences were not linked to DNA DSB induction or repair but correlated with micronucleus formation, indicating chromosome damage.

Conclusions:

• Cell killing by 125I is not solely determined by the number of DNA double-strand breaks (DSBs).
• Damage to higher-order genome structures may play a significant role in radiation-induced cell death.
• HAT medium exposure alters the cellular response to 125I radiation, impacting cell survival pathways.