DNA methylation changes following DNA damage in prostate cancer cells

Area of Science:

• Cancer Biology
• Epigenetics
• Radiation Oncology

Background:

• Cancer therapies often induce DNA double-strand breaks (DSBs) to kill cells.
• Treatment-resistant cancers survive by efficiently repairing DSBs.
• The role of the epigenome, particularly DNA methylation, in this repair process is not well understood.

Purpose of the Study:

• To investigate the impact of radiotherapy on DNA methylation profiles in prostate cancer cells.
• To examine the influence of DNA methylation on DSB formation and repair following radiation.
• To assess the effect of the hypomethylating agent 5-azacytidine on radioresistant cells.

Main Methods:

• Analysis of DNA methylation profiles using the Illumina Infinium HumanMethylation450 BeadChip.
• Assessment of DSB formation and repair via γH2A.X immunofluorescence staining.
• Treatment of prostate cancer cell lines with radiotherapy (RT) and 5-azacytidine (5-AzaC).

Main Results:

• A single dose of RT caused minor, stable alterations in DNA methylation at specific CpG sites up to 14 days post-exposure.
• Distinct basal DNA methylation profiles existed between radioresistant and radiosensitive cells, but DSB susceptibility and repair were similar.
• 5-AzaC treatment did not sensitize resistant cells; instead, it delayed the recruitment of phosphorylated BRCA1 and DSB repair.

Conclusions:

• Stable epigenetic changes can occur after a single RT dose, with potential clinical implications for fractionated or recurrent dosing.
• Basal DNA methylation appears to have a limited role in DSB induction and initial repair in the examined prostate cancer models.
• Hypomethylating agents may interfere with DNA repair pathways, warranting caution in combination cancer therapies.