Lizhu Chen,1– 3,* Jing Lin,1– 3,* Yaoming Wen,4,* Zeng-Qing Guo,1– 3,* Bin Lan,2,3 Jiani Xiong,1– 3 Chuan-Ben Chen,2,3,5 Yu Chen1– 3 

1Department of Medical Oncology, Clinical Oncology School of Fujian Medical University, Fujian Cancer Hospital, Fuzhou, Fujian Province, People’s Republic of China; 2Cancer Bio-Immunotherapy Center, Clinical Oncology School of Fujian Medical University & Fujian Cancer Hospital, Fuzhou, Fujian Province, People’s Republic of China; 3Fujian Provincial Key Laboratory of Translational Cancer Medicine, Clinical Oncology School of Fujian Medical University & Fujian Cancer Hospital, Fuzhou, Fujian Province, People’s Republic of China; 4Department of Drug Research and Development, Fujian Institute of microbiology, Fuzhou, Fujian Province, People’s Republic of China; 5Department of Radiation Oncology, Clinical Oncology School of Fujian Medical University, Fujian Cancer Hospital, Fuzhou, Fujian Province, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Yu Chen; Chuan-Ben Chen, Email chenyu1980@fjmu.edu; ccb@fjmu.edu.cn

Introduction: Combining radiotherapy (RT) with immunotherapy for head and neck squamous cell carcinoma (HNSCC) has limited effectiveness due to the DNA damage repair (DDR) pathway activated by ionizing radiation. DNA-PK, encoded by the PRKDC gene, plays a key role in this repair. The potential improvement of radioimmunotherapy by inhibiting the DDR pathway is still unclear.
Methods: The effectiveness of different treatments on tumor growth and survival was tested using the C3H/HeN mouse tumor model. Flow cytometry analyzed treatment-induced immunophenotypic changes. In vitro, Western blot and PCR confirmed the impact of combining immunotherapy with RT on the cGAS-STING pathway after DNA-PKcs dysfunction.
Results: The combination of a DNA-PK inhibitor (NU7441), radiation therapy, and a PD-1 checkpoint inhibitor showed improved antitumor effects and extended survival in mice. Adding NU7441 into the RT and immunotherapy regimen increased CD8+ T cell infiltration. PRKDC alterations or DNA-PKcs dysfunction increased IR-induced DNA breaks, activating the cGAS-STING pathway and boosting the anti-tumor immune response.
Conclusion: These findings suggest that targeting the DDR pathway may represent a promising therapeutic strategy and biomarker to improve the efficacy of radioimmunotherapy in HNSCC.

Keywords: head and neck squamous cell carcinoma, PRKDC, cGAS-STING, radioimmunotherapy, DNA-PK