Targeting OGG1 and PARG radiosensitises head and neck cancer cells to high-LET protons through complex DNA damage persistence

Complex DNA damage (CDD), characterized by two or more lesions within one or two helical turns of DNA, is a hallmark of ionizing radiation (IR) and plays a significant role in its therapeutic effectiveness through cell killing. The levels and complexity of CDD increase with linear energy transfer (LET). However, the specific cellular responses to this type of damage and the critical proteins involved in its repair remain unclear.

To address this, we conducted an siRNA screen targeting approximately 240 DNA damage response proteins to identify those crucial for cell survival following high-LET protons at the Bragg peak, in contrast to low-LET entrance dose protons, which generate different levels of CDD. Our validation studies revealed that depleting 8-oxoguanine DNA glycosylase (OGG1) and poly(ADP-ribose) glycohydrolase (PARG) in HeLa and head and neck cancer cells significantly increased radiosensitivity specifically after exposure to high-LET protons, with no observable effect after low-LET protons or X-rays.

We confirmed that both OGG1 and PARG are essential for efficient repair of CDD following irradiation with high-LET protons. Importantly, these findings were also supported by using specific inhibitors for OGG1 (TH5487) and PARG (PDD00017273). Our results indicate that OGG1 and PARG are critical to the cellular response to CDD, suggesting that targeting these enzymes could be a promising therapeutic strategy for treating head and neck cancers after high-LET radiation exposure.