Chao Mao, Shengrong Wu, Girish H. Rajacharya, Min Wang, Zhengze Lu, David Huo, Yuelong Yan, Xiong Chen, Guang Lei, Zhihao Xu, Qidong Li, Mingchuang Sun, Xi Zhao, Li Zhuang, Dadi Jiang, Steven H. Lin, Albert C. Koong, Pankaj K. Singh, Boyi Gan
Radiotherapy (RT) is a mainstay in the treatment of solid tumors, including lung cancer, yet the long-term efficacy is often limited by radioresistance. RT promotes multiple different cell death processes, and gaining mechanistic insights into how metabolic cell death pathways like ferroptosis contribute to resistance could enable the development of effective modulators of radiation sensitivity. In this study, through metabolomic and functional analyses, we identified dihydroorotate dehydrogenase (DHODH) as a critical regulator of radioresistance in lung cancer. DHODH expression was induced by radiation in a cAMP response element-binding protein-dependent manner, and both radiation exposure and acquired radioresistant states were associated with elevated DHODH activity. DHODH promoted radioresistance in part by generating ubiquinol, a mitochondrial lipid antioxidant that suppresses ferroptosis, and by supporting DNA repair through its role in de novo pyrimidine synthesis. Although DHODH inhibition alone had limited therapeutic effect, its combination with interferon-gamma (IFNγ; delivered directly or via anti-PD-1 immunotherapy) synergistically enhanced RT-induced ferroptosis and overcame radioresistance in preclinical models. These findings reveal a metabolic mechanism of radioresistance driven by DHODH-mediated ferroptosis defense and provide a rationale for combining DHODH inhibitors with RT and immunotherapy in lung cancer and potentially other solid tumors. SIGNIFICANCE: DHODH acts as a metabolic barrier to ferroptosis-driven radiosensitivity and can be targeted in combination with radiotherapy and immunotherapy as a strategy for treating lung cancer.