Abstract 6032: Establishment of a bladder cancer model using organoids derived from bladder epithelium in genetically engineered mice

Abstract Despite recent advances in molecular profiling of bladder cancer, molecular mechanisms for urothelial carcinogenesis have not fully understood. It is partly because the lack of faithful disease models that accurately recapitulate human bladder cancer. In our previous study, we have analyzed mutation landscape of chemical-induced mouse bladder cancer and human bladder cancer by exome-sequence and found that some components of histone methyltransferase complex like Kmt2c, Kmt2d, Kdm6a were highly prevalent as common mutations and associated with Trp53. Additionally, the downregulation of tumor suppressor gene PTEN is known in human muscle invasive bladder cancer (MIBC). We also investigated cell of origin of chemical-induced mouse bladder cancer using lineage tracing method and found that Krt5 expressing cells with Trp53 alteration efficiently give a rise of high-grade MIBC with squamous differentiation. Based on these results, we have tried to make MIBC mouse model using genetically engineered mouse in which Cas9 and target gene mutation express specifically in Krt5 expressing cells by Cre-LoxP system, combined with CRISPR/Cas9 gene editing technique and 3D organoid culture system. Eight-week-old mice harboring Krt5CreERT2/+; LSL-Cas9; LSL-Trp53+/R172H were used in this study. After introducing gene recombination by administration of tamoxifen, we generated organoids from bladder epithelial cells. For further gene editing, we infected adeno-associated virus with sgPten and sgMll3 to the organoids, which successfully edited the target genes. There seemed to be no significant differences in growth of the organoids in culture between the wild-type and gene-edited organoids. However, gene-edited organoids showed tumorigenesis in vivo when inoculated in subcutaneous space, renal subcapsular space or bladder submucosa of athymic mice, whereas wild-type organoids did not show tumorigenesis in vivo. Histologically, the organoid-derived tumors showed morphological similarity to human urothelial carcinoma with squamous differentiation and intra-tumoral heterogeneity. Furthermore, tumor derived organoid has a potential of tumor development in immune-competent mice. These tumors also maintain squamous phenotype and tumor heterogeneity. These findings suggest that the technique is a promising approach toward the establishment of a useful model of human bladder cancer for the elucidation of bladder carcinogenesis including driver genes. In addition, we think our syngeneic mouse model may be useful tool for further research of tumor immunity and immune checkpoint inhibitor drugs. Citation Format: Akihiro Hamada, Yuki Kita, Hideaki Takada, Kenji Nakamura, Toru Sakatani, Takeshi Sano, Takayuki Goto, Atsuro Sawada, Shusuke Akamatsu, Takashi Kobayashi. Establishment of a bladder cancer model using organoids derived from bladder epithelium in genetically engineered mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6032.