Low-dose radiation hypersensitivity is associated with p53-dependent apoptosis

Area of Science:

• Radiation biology
• Cellular and molecular oncology

Background:

• Environmental radiation and radioimmunotherapy necessitate understanding cellular responses to low-dose ionizing radiation.
• Tumor cell lines exhibit hypersensitivity to radiation doses below 50 cGy, deviating from predicted survival curves.
• The biological mechanisms underlying low-dose hypersensitivity remain largely unknown.

Purpose of the Study:

• To investigate the cellular mechanisms responsible for hypersensitivity to low-dose and low-dose rate ionizing radiation.
• To determine the role of p53 in mediating low-dose hypersensitivity and associated cellular responses.

Main Methods:

• Utilized a gel microdrop/flow cytometry assay to monitor single-cell proliferation post-irradiation.
• Assessed cell cycle status, apoptosis (caspase-3 activation, Annexin V binding) in response to gamma radiation (0-200 cGy at 0.18 and 22 cGy/min).
• Investigated the effect of pifithrin (p53 inhibitor) on low-dose hypersensitivity and apoptosis in p53-proficient and p53-inactive cell lines.

Main Results:

• A549 lung carcinoma and T98G glioma cells displayed hypersensitivity to <50 cGy radiation, unlike MCF7 breast carcinoma cells.
• Low-dose radiation-induced hypersensitivity correlated with increased caspase-3 activation and Annexin V binding.
• Pifithrin treatment abolished low-dose hypersensitivity and apoptosis in A549 and T98G cells.
• p53-inactive cell lines (2800T fibroblasts, HCT116 carcinoma) did not exhibit hyperradiosensitivity or detectable apoptosis.

Conclusions:

• Low-dose hypersensitivity in certain human tumor cell lines is dependent on functional p53.
• p53-mediated apoptosis plays a critical role in the observed hyperradiosensitivity phenomenon.
• These findings provide insight into cellular responses to low-dose radiation, relevant for clinical applications.