DNA damage induced by nitric oxide during ionizing radiation is enhanced at replication

Area of Science:

• Molecular Biology
• Radiation Oncology
• Biochemistry

Background:

• Nitric oxide (NO) is a potent radiosensitizer for hypoxic mammalian cells.
• NO's mechanism involves DNA base damage, potentially leading to replication-induced strand breaks.
• Previous studies identified reactions of guanine radicals with NO.

Purpose of the Study:

• To investigate the reaction of adenine radicals with NO.
• To elucidate the role of NO in inducing specific DNA damage and cell death.
• To compare radiosensitization by NO in dividing versus confluent cells.

Main Methods:

• Studied the reaction of adenine radicals with nitric oxide (NO).
• Irradiated mammalian cells (V79-4, HF-19) in the presence of NO under varying conditions (anoxia, exponential vs. confluent growth).
• Assessed DNA damage using markers like γH2AX and 53BP1 foci, and replication fork integrity via RAD51 foci.

Main Results:

• Adenine radicals react with NO to form hypoxanthine and 8-azaadenine.
• NO-treated exponentially growing cells showed doubled radiosensitivity compared to anoxia alone.
• Increased DNA double-strand breaks (γH2AX), DNA damage (53BP1), and stalled replication forks (RAD51) were observed in NO-treated dividing cells.

Conclusions:

• Radiosensitization by NO is partly mediated by the formation of specific, hard-to-repair DNA damage.
• This DNA damage can induce stalled replication forks and replication-induced DNA strand breaks in dividing cells.
• NO-induced DNA damage contributes to cell death, highlighting its potential as a radiosensitizer in cancer therapy.