Abstract 4261: Synthetic lethality of targeting thymine DNA glycosylase (TDG) in p53-deficient lung cancer

Abstract TP53 stands as the most frequently mutated gene in human cancers, with a strong correlation to poor prognosis across various cancer types. This makes it a critical target, representing the largest patient population and a substantial tumor drug market, with a pressing unmet medical need. Directly targeting p53 remains highly challenging, leaving a significant therapeutic gap. However, synthetic lethality presents a promising approach for developing treatments targeting tumors with TP53 mutations. Thymine DNA glycosylase (TDG) is a multifaceted enzyme involved in DNA base excision repair (BER), transcriptional regulation, and DNA demethylation, playing critical roles in both embryonic development and tumor progression. In this study, we identified TDG as a synthetic essential effector in p53-deficient cancers. This identification was facilitated through an in vitro CRISPR-Cas9 screening assay conducted in Trp53 knockout cells. Our finding reveals that knocking out Tdg selectively kills p53-deficient cells while sparing wild-type cells. Conversely, knocking out Trp53 selectively kills Tdg-deficient cells. Furthermore, elevated TDG expression was observed to correlate with p53-deficiency in human cancers. TDG knockout significantly reduced the viability of the p53-deficient lung cancer cell line NCI-H1299, an effect was rescued by ectopic expression of wild-type p53, but did not affect the viability of p53 wide-type cell line A549. Using a genetically engineered mouse model of lung adenocarcinoma (LUAD), we further demonstrated that genetic inactivation of Tdg specifically suppressed tumor growth in the context of p53-deficiency. Mechanistically, TDG and p53 cooperate to regulate the transcription of the RNA helicase DHX9, which facilitates the resolution of double-strand RNA (dsRNA). Inhibition of TDG in p53-deficient cancer cells downregulated DHX9, leading to aberrant accumulation of dsRNA derived from SINEs (short interspersed nuclear elements). This accumulation triggered an anti-viral response via the RIG-I/MDA5-MAVS axis, resulting in tumor growth inhibition and an enhanced anti-tumor immune response. Notably, the dsRNA-mediated antiviral response induced by Tdg depletion facilitated the recruitment of tumor-infiltrating lymphocytes (TILs), enhancing response to immune checkpoint blockade (ICB) treatment. These findings reveal a novel therapeutic vulnerability in p53-deficient lung cancer and suggest that targeting TDG could synergize with immunotherapies to improve patient outcomes. Our study highlights the function of TDG in transcriptional regulation, extending beyond its proposed roles in active DNA demethylation and mismatch repair, and unveils TDG as a promising therapeutic target for p53-deficient lung cancer. Citation Format: Jiaxin Zhou, Zhenyu Shao, Jiannan Guo, Yiqin Wang, Qing Xu, Yarui Du, Haiping Wu, Guoliang Xu. Synthetic lethality of targeting thymine DNA glycosylase (TDG) in p53-deficient lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4261.