Abstract B025: Luminal-to-basal phenotypic plasticity promotes invasive phenotypes in a live-imaging assay using patient-derived bladder tumor organoids
Authors: Coz Clementine Le , Christin John R. , Syed Talal , Wang Zejian , Laplaca Caroline J. , Lenis Andrew T. , Shen Michael M. 
Published: May 2024

Abstract
Lineage plasticity in cancer is characterized by changes in cell state that are often associated with tumor progression and treatment resistance. While nearly all non-muscle invasive bladder cancer (NMIBC) tumors have a luminal epithelial phenotype, many muscle invasive bladder cancers (MIBC) display a basal identity. NMIBC to MIBC progression may therefore be related to a phenotypic switch from luminal-to-basal subtypes, which in turn may be associated with poorer clinical outcomes. However, current understanding of the molecular processes linking cell plasticity and tumor invasion is limited, due in part to a lack of physiologically relevant in vitro models and assays. To address these questions, we are utilizing a living biobank of 82 patient-derived bladder tumor organoid lines that our group has established. These organoids represent a 3-dimensional, heterogeneous model system for studying bladder cancer, as they can be genetically manipulated and recapitulate the molecular and histopathological features of the parental tumor. Notably, in previous work, we described luminal-to-basal phenotypic plasticity in a subset of organoid lines derived from luminal tumors, which display a shift to basal/squamous identity in culture that is reversible by orthotopic xenografting. In current studies, we are investigating cell migration and invasiveness using a live-imaging assay that we have developed to examine bladder tumor organoid outgrowth in vitro. Importantly, this assay allows longitudinal visualization as well as quantitation of invasiveness over a four-day time span. Analysis of over 25 organoid lines with plastic, stable luminal, and stable basal properties has revealed a broad spectrum of organoid outgrowth phenotypes that do not correlate with cell proliferation or clinical parameters. Instead, the degree of outgrowth correlates precisely with luminal-to-basal phenotypic plasticity, as assessed by transcriptome analyses, immunofluorescence microscopy, and in vivo xenografting. Organoid lines with minimal outgrowth have stable luminal phenotypes, whereas lines that produce their own extracellular matrix to create a leading edge of migrating cells have plastic phenotypes. Furthermore, movies of the invading organoids reveal distinct cell migratory patterns, as several organoid lines display collective migration that generates an invasive front at the leading edge. This collective migration phenotype is distinct from phenotypic plasticity, is at least partially independent from organoid outgrowth, and is undergoing further analysis. Thus, our organoid outgrowth assay identifies two different parameters of invasive potential, one of which correlates with phenotypic plasticity. Our findings characterize bladder tumor invasion patterns for the first time and suggest that lineage plasticity in NMIBC represents a key mechanism that promotes tumor invasion in MIBC.
Citation Format: Clementine Le Coz, John R. Christin, Talal Syed, Zejian Wang, Caroline J. Laplaca, Andrew T. Lenis, Michael M. Shen. Luminal-to-basal phenotypic plasticity promotes invasive phenotypes in a live-imaging assay using patient-derived bladder tumor organoids [abstract]. In: Proceedings of the AACR Special Conference on Bladder Cancer: Transforming the Field; 2024 May 17-20; Charlotte, NC. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(10_Suppl):Abstract nr B025.