Targeting DNA Damage Response Dependencies for Radiosensitization in Li-Fraumeni Syndrome

Li-Fraumeni Syndrome (LFS) is a hereditary cancer predisposition syndrome associated with germline TP53 mutations, leading to a significantly increased lifetime cancer risk. Individuals with LFS display striking clinical heterogeneity, including variation in tumour onset, aggressiveness, and metastasis, highlighting the need to better understand genetic modifiers and their influence on cancer susceptibility. Recent work from our lab suggests that variation in Wnt signalling may be contributing to this clinical diversity. The Wnt pathway regulates many cellular processes, including proliferation, differentiation, and stemness. When hyperactivated, it can promote oncogenesis by stabilizing beta-catenin levels, activating transcriptional programs that support tumour initiation and progression. Whole-genome sequencing on a large, multi-institutional cohort of LFS patients has identified Wnt-pathway variants that appear to decrease cancer risk and are associated with improved survival. These variants are predicted to dampen beta-catenin signalling, pointing toward a novel mechanism that may act to counterbalance TP53-driven oncogenesis. To further investigate the differences contributing to heterogeneity in LFS, we are developing a proteomic atlas of patient-derived dermal fibroblasts, representing a range of clinical presentations: wild-type (n=5), clinically unaffected LFS carriers (n=7), and LFS individuals with known malignancies (n=6). Baseline protein expression was quantified using mass spectrometry, and Wnt-related proteins were identified for further testing. To explore the functional mechanisms of these variants, siRNA-mediated knockdowns will be used to examine how short-term reductions in Wnt expression affect cancer-associated cell phenotypes. Preliminary analyses have identified that LFS fibroblasts demonstrate increased expression of Wnt receptors compared to wild-type, suggesting a baseline priming towards Wnt activation. Gene set enrichment analysis demonstrated an enrichment of beta-catenin, Lef1, and Myc transcriptional programs in LFS cells, consistent with a strongly activated Wnt signalling state. Together, these findings support hyperactive Wnt signalling as a defining feature of the LFS cellular environment and a contributing factor to TP53-driven oncogenesis. By integrating proteomic profiling with functional variant validation, this work examines how Wnt-modifying variants contribute to the tumorigenic environment in LFS. The results of this study will help us to better understand the biological heterogeneity seen among LFS patients and lay the groundwork for future research into Wnt modifiers as therapeutic interventions. Beyond the scope of this project, the LFS fibroblast proteomic atlas may act as a novel resource for the LFS and TP53 research communities, providing unbiased quantification of proteins across different clinical outcomes.