Abstract LB092: Decoding tumor cell dynamics driven by mutant <i>TP53</i> gain-of-function activity in squamous cell carcinoma metastasis

Abstract Mutations in the tumor suppressor gene TP53 correlate with poor prognosis and high metastasis rates, which account for more than 90% of cancer-related mortality worldwide. Our recent work, published in Cancer Discovery (PMC10841313), highlights that mutant TP53 may exhibit neomorphic gain-of-function (GOF) properties, driving squamous cell carcinoma (SCC) metastasis beyond its classic role via wild-type TP53 loss. To elucidate novel mutant p53-dependent mechanisms in promoting metastasis, we first focused on one of the most frequent TP53 mutations, human R175H (mouse homolog, R172H). Utilizing the L2-Cre (esophageal specific promoter), we generated LSL-Trp53 R172H/- , Trp53 -/- or Trp53 +/+ mice to isolate isogenic primary and metastatic tumor cells that vary in their p53 statuses. Using ex vivo and in vivo syngeneic models, we found that p53-R172H significantly enhances metastatic colonization in the lung compared to tumor cells with wild-type p53 or p53-null, suggesting GOF features of this mutant protein. Through our analysis of RNA-Seq, p53 ChIP-Seq, and H3K27ac CUT&amp;RUN-Seq on metastatic tumor cells, we identified mediators of the epithelial-to-mesenchymal transition (EMT) pathway as dominant effectors of p53-R172H-dependent lung metastasis. While most research efforts have traditionally focused on a single mutation, our studies now leverage to an evaluation of the mutant TP53 spectrum to assess how each specific mutation may contribute to unique pro-tumorigenic activities. Our analysis of aero-digestive SCC datasets from AACR Project Genie, TCGA, and tissue microarrays suggests that recurrently detected TP53 mutations are associated with differential patient survival rates and enriched molecular pathways. To investigate the extent of GOF properties and underlying mechanisms of distinct TP53 mutations, we endogenously introduced four frequently detected mutations (R175H, R248Q, R273H and R282W) into esophageal SCC (ESCC) mouse and human cells using state-of-the-art genome engineering approaches. This has allowed us to generate a physiologically relevant and isogenic model. Tumors harboring different TP53 mutations demonstrate varying degrees of enhanced invasion and metastatic abilities in comparison to TP53-deleted controls. Among these, TP53 R282W mutant tumor cells show a marked increase in lung metastases, accompanied by the enrichment of inflammatory response and interferon-alpha response pathways. Our molecular analyses of diverse TP53 mutations provide new insights into their GOF properties. TP53 mutations exhibit distinct clinical outcomes, as well as unique functional and mechanistic behaviors, emphasizing the need for allele-specific mutational analysis in therapeutic strategies. Identifying actionable downstream targets regulated by specific TP53 mutations could transform precision medicine efforts. Furthermore, this approach can be extended to key oncoproteins involved in critical signaling pathways, such as KRAS and PIK3CA. Citation Format: Gizem Efe, Katherine Cunningham, Raúl Navaridas, Karen Dunbar, Emily Esquea, Lois Resnick-Silverman, James J. Manfredi, Carol Prives, Anil K. Rustgi. Decoding tumor cell dynamics driven by mutant TP53 gain-of-function activity in squamous cell carcinoma metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_2):Abstract nr LB092.