Abstract 1436: Cancer associated fibroblast dependency in a model of bladder cancer

Abstract Introduction: The relationship between genotype and phenotype in targeted therapy has proven to be crucial for most kinase inhibitors. In bladder cancer, the PI3K/AKT/mTOR pathway is widely activated by mutation but untargeted. Our study focuses on developing an immunocompetent, CRISPR-edited bladder cancer mouse model that mirrors common PI3K/AKT/mTOR mutations. We aim to establish genotype-effective kinase inhibitor pairings using in vitro CRISPR-edited organoids and Cancer Associated Fibroblasts (CAFs) to create a pro-tumorigenic environment in vivo. Methods and Results: Urothelial cells were isolated from the bladder of Rosa26 Lox-Stop-Lox-Cas9/GFP transgenic mice to develop organoids. These organoids were co-edited for Trp53 and Rb1 KO, and further editing of the Pten gene resulted in a nine-fold increase in sensitivity to the kinase inhibitor ipatasertib. Despite successful engraftment into mouse bladder, these edited cells regressed before tumor formation, and intradermal injection did not yield subcutaneous tumors. An alternate model featuring a 9p21 deletion with Trp53 KO also displayed similar regression post-engraftment into bladder or skin. However, co-injection with skin-cancer-derived CAFs subcutaneously yielded palpable subcutaneous tumors that grew for 12 weeks. Enhancing orthotopic model fidelity, we established a BBN bladder-tumor-derived CAF line, leading to the formation of tumors with squamous differentiation upon intramural co-injection with edited organoids. These models displayed immune-excluded architecture and a predominance of M2 over M1 macrophages. Following our accomplishments in establishing bladder tumors, we aimed to enhance our model's adaptability by introducing common PI3K/AKT/mTOR mutations, specifically TSC1/TSC2 KO and Pik3ca hotspots, into our 9p21/Trp53 KO model. While TSC1/TSC2 KO lines exhibited elevated P-S6K signaling, they displayed resistance to Torin 1, Voxtalisib, and Everolimus—kinase inhibitors targeting mTORC1/2. In parallel, we employed CRISPR-mediated HDR to successfully introduce a Pik3ca H1047R hotspot into our 9p21/Trp53 KO model, as evidenced by increased Phosphorylation of AKT compared to wild-type 9p21/Trp53 KO cell lines. Conclusions: Our research establishes the crucial role of CAFs in bladder tumor formation. Our now established customizable model of bladder cancer is suitable for direct targeting by kinase inhibitors while providing a platform for understanding the genotype-phenotype relationship in bladder cancer. Citation Format: Henkel Valentine, Uttam Satyal, Laura Bukavina, Hassan Uddin, Yousttena Beyamin, Rhea Arya, Philip Abbosh. Cancer associated fibroblast dependency in a model of bladder cancer 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 (6Suppl): Abstract nr 1436.