TP53 modulates radiotherapy fraction size sensitivity in normal and malignant cells

Area of Science:

• Radiation oncology
• Molecular biology
• Cancer research

Background:

• Current radiotherapy practices use standardized fraction sizes, not personalized to individual patient molecular profiles.
• Understanding the mechanisms of fraction size sensitivity is crucial for optimizing radiotherapy efficacy and patient outcomes.
• Wild-type p53 and non-homologous end-joining (NHEJ) are key cellular components involved in DNA damage response.

Purpose of the Study:

• To investigate the role of wild-type p53 and intact NHEJ in determining cellular sensitivity to radiotherapy fraction size.
• To explore how defects in p53 or NHEJ influence the cellular response to fractionated radiation doses.

Main Methods:

• Utilized colony-survival assays to assess split-dose recovery in various normal and malignant cell lines following single or split radiation doses.
• Employed siRNA knockdown of p53 and DNA-PKcs inhibitors to study their effects on fraction size sensitivity.
• Examined cells with known defects in p53 or NHEJ pathways, including Li-Fraumeni fibroblasts and DNA repair-deficient cell lines.

Main Results:

• Cells with wild-type p53 exhibited significant split-dose recovery, indicating a sparing effect from fractionated radiotherapy.
• Cells with defective p53 or impaired G1/S checkpoint showed reduced split-dose recovery and lost the sparing effect of smaller fractions.
• NHEJ-deficient cells (DNA ligase IV and DNA-PKcs mutants) lacked split-dose recovery, and DNA-PKcs inhibition increased sensitivity to split doses in glioma cells.
• siRNA-mediated knockdown of p53 in fibroblasts decreased split-dose recovery.

Conclusions:

• Radiotherapy fraction size sensitivity is significantly dependent on the presence of functional wild-type p53.
• Intact non-homologous end-joining (NHEJ) DNA repair is essential for the sparing effect observed with fractionated radiotherapy.
• These findings highlight the potential for personalized radiotherapy strategies based on a patient's p53 and NHEJ status.