Abstract 6405: Identification of molecular targets in bladder cancer variants using single-cell analysis

Abstract Introduction and objectives: Variant subtypes in bladder cancer, also known as histologic variants, are clinically aggressive tumors associated with poor prognosis. The rarity of these tumors has made molecular characterization elusive using bulk transcriptional profiling. The aim of this study was to use single cell RNA sequencing to identify molecular features associated with variant subtypes that could be potential targets for therapy. Methods: Fresh tissue from bladder cancer patients undergoing surgery at our institution was sequenced using a bead-based single-cell RNA sequencing platform (Seq-Well) to generate an atlas of 9 tumors containing variants (micropapillary, nested, squamous differentiation, pleomorphic giant-cell like, plasmacytoid, small cell) and 3 tumors with pure urothelial carcinoma (UC) histology. Pathologic diagnoses were independently confirmed. Analysis was performed using the Seurat package in R Studio. Immunostaining validation was performed on a separately banked cohort. Bulk RNA sequencing data and clinical data were extracted and analyzed from The Cancer Genome Atlas (TCGA) database. Chimeric Antigen Receptor (CAR) T cells targeting TM4SF1 were generated by lentiviral transduction of primary human T cells and tested against publicly available bladder cancer cell lines. Results: Variant tumors were enriched in TM4SF1, a surface molecule that we demonstrate to be susceptible to CAR T therapy in vitro. Variants also share a cell state characterized by highly specific expression of MUC16 (CA125), which is enriched in metastatic sites, harbors transcriptional hallmarks of epithelial-mesenchymal transition and luminal-basal plasticity, and is associated with poor survival and resistance to chemotherapy. Finally, we find evidence of transcriptional mimicry between variants and similar appearing non-urothelial cells (e.g. plasmacytoid:plasma cell), suggesting common pathways between distinct cell types that could be exploited. Conclusion: We have identified several targetable molecular features within variant bladder cancer subtypes. These findings set a critical starting point for future therapeutic investigation. Funding: California Urology Foundation (HY)Conflicts of interest: noneKeywords: Single cell analysis, bladder cancer, variants, genomics, biomarkers Citation Format: Heiko Yang, Hanbing Song, Paul Allegakoen, Kevin Lu, Elizabeth Yip, Keliana Hui, Kevin Chang, Corynn Kasap, Janae Gayle, Bradley Stohr, Arun Wiita, Chien-Kuang C. Ding, Maxwell V. Meng, Jonathan Chou, Sima P. Porten, Franklin W. Huang. Identification of molecular targets in bladder cancer variants using single-cell analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6405.