Abstract PS4-10-23: Uncovering Mechanisms Driving Phenotypic Distinctions between Breast Cancer Cells with Different p53 Mutations using a 3D Microfluidic Platform

Abstract TP53 is the most mutated gene in cancer, with alterations present in roughly 50% of all cancer cases and in approximately 80% of the aggressive Triple Negative Breast Cancer (TNBC). The wild type p53 protein plays a vital role in suppressing cancer by promoting DNA damage repair, regulating cell cycle arrest, inducing apoptosis, and inhibiting cell invasion among other functions. Most of these mutations are single amino acid substitutions, occurring in more than 130 forms and contributing to tumor heterogeneity with potential neomorphic activities. However, despite ongoing efforts of developing precision therapeutics for TNBC, the functional impacts of individual mutant p53 as distinct cancer drivers remain poorly understood. Previously, we created a cell line panel with ten p53 mutations common in breast cancer and reported that each mutation led to distinct molecular and phenotypic profiles. Our current study focuses on the R273C and Y234C mutants, which were the most and least invasive, respectively, to identify the underlying mechanisms of phenotypic heterogeneity and potential drug targets. We have employed a 3D tumor-on-chip technology, which offers detailed single-cell-level insights in more in-vivo-like conditions, and observed highly distinct cellular behaviors of R273C cells with mesenchymal morphology and reduced proliferation, compared to cells with wild-type p53 or Y234C mutant that formed large acini-like structures. Immunostaining and RNA-Seq analyses confirmed further that R273C strongly induced epithelial-to-mesenchymal transition (EMT) and gene expression profile changes similar to those of metastatic breast cancer cells such as MB-231. Using the RNA-Seq data, we have identified differentially regulated genes and pathways in R273C and Y234C. We are currently working on mechanistic investigation to understand how the R273C mutant induces EMT and identification/validation of the top candidates that can potentially intervene in TNBC with more aggressive p53 mutations. Citation Format: L. Sakala, K. Ravi, Y. Zhang, E. Hurt, J. G. Park, M. Nikkhah, J. LaBaer. Uncovering Mechanisms Driving Phenotypic Distinctions between Breast Cancer Cells with Different p53 Mutations using a 3D Microfluidic Platform abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS4-10-23.