FLASH-RT does not affect chromosome translocations and junction structures beyond that of CONV-RT dose-rates

Area of Science:

• Radiation Oncology
• Molecular Biology
• Genetics

Background:

• Radiotherapy (RT) uses high-energy radiation to kill cancer cells.
• Investigating the impact of ultra-high dose rate (FLASH) versus conventional dose rate (CONV) RT on DNA damage is crucial.
• The generation and repair of DNA double-strand breaks (DSBs) are key outcomes of RT.

Purpose of the Study:

• To test the hypothesis that FLASH-RT generates fewer chromosomal translocations than CONV-RT.
• To compare DNA double-strand break repair and translocation formation between FLASH-RT and CONV-RT.
• To evaluate the influence of varying oxygen tensions on these processes.

Main Methods:

• Utilized FLASH-validated electron beams and high-throughput genome-wide translocation sequencing (HTGTS-JoinT-seq) in HEK293T cells.
• Introduced Cas9 "bait" DSBs to measure bait-proximal repair and genome-wide translocations to "prey" DSBs.
• Irradiated cells at CONV (0.08-0.13 Gy/s) and FLASH (1x10^2-5x10^6 Gy/s) dose rates under normoxic, physioxic, and hypoxic conditions.
• Assessed clonogenic survival and γH2AX foci in 293T and U87 glioblastoma cells.

Main Results:

• Normoxic and physioxic irradiation increased translocations and decreased bait-proximal repair, with no difference between CONV-RT and FLASH-RT.
• Hypoxia did not increase chromosome translocations, and dose rate modulation under hypoxia showed no significant differences in translocation levels or junction structures.
• FLASH-RT vs. CONV-RT did not alter γH2AX foci numbers or 293T clonogenic survival.

Conclusions:

• FLASH-RT produces chromosomal translocations and junction structures at levels indistinguishable from CONV-RT.
• Oxygen tension does not alter the comparable translocation outcomes between FLASH-RT and CONV-RT.
• The DNA damage and repair profiles are similar between FLASH-RT and CONV-RT across different conditions.