Abstract 3932: Elucidating mechanisms of metastatic progression in bladder cancer with novel GEMMs and systems biology approaches

Abstract Metastasis is the leading cause of bladder cancer deaths. Despite recent advances in treatment, metastatic bladder cancer remains incurable. One of the major challenges in studying metastasis has been the lack of suitable in vivo models that recapitulate the natural evolution of metastatic progression within the native tumor microenvironment. To address this, we have generated genetically-engineered mouse models (GEMMs) of bladder cancer that have highly penetrant metastatic phenotypes. In particular, our new metastatic GEMMs build on our previously established GEMM, in which bladder-specific co-inactivation of Pten and p53 (double knockout, DKO), leads to muscle-invasive bladder cancer (MIBC) with a low incidence of metastasis. By introducing loss-of-function mutations in Arid1a, an epigenetic regulator that is frequently mutated in high-grade human bladder cancer, we generated triple knockout (TKO) mice. These mice develop highly lethal MIBC with over 80% incidence of regional and distant metastasis. Histopathological characterization of TKO tumors revealed aggressive features, including aberrant differentiation and enhanced invasiveness, and demonstrated strong conservation with human MIBC, as shown by the expression of basal and luminal subtype markers. We implemented a systems biology approach to identify mechanistic determinants, or master regulators (MRs), of metastasis. To identify drivers of metastatic progression, we first performed RNA sequencing to compare metastatic tumors with pre-tumor bladder urothelium from TKO mice. Gene signatures from TKO tumors were highly conserved with human MIBC. Cross-species analysis integrating TKO mouse data with human bladder cancer datasets identified conserved MRs predictive of adverse outcome in several independent patient cohorts. Key regulators of bladder cancer, such as Pparg and Shh, and lineage plasticity drivers, like Sox11, emerged as candidates. To prioritize these MRs, we performed CRISPR-based functional screening, which highlighted promising targets that are now being evaluated in our mouse models. In summary, we developed GEMMs that faithfully model metastatic bladder cancer. Our cross-species analysis identified a panel of conserved MRs, including Pparg, Shh, and Sox11, as key drivers of lineage plasticity and metastatic progression. These findings offer insights into the mechanisms of bladder cancer metastasis and suggest novel therapeutic opportunities. Citation Format: Siyue Lin, Soonbum Park, Alexander Chui, John R. Christin, Andrea Califano, Michael M. Shen, Cory Abate-Shen. Elucidating mechanisms of metastatic progression in bladder cancer with novel GEMMs and systems biology approaches [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 3932.