Abstract B13: A novel mouse model for small-cell carcinoma of bladder

Background: Molecular characterization studies suggest the neuronal subtype muscle invasive bladder cancer (MIBC) is associated with a high response rate to immune checkpoint inhibitor. We sought to establish a mouse model for small-cell carcinoma of bladder. Materials and Methods: Three canonical signaling pathways (TP53, RB1, and RTK/PI3K/AKT) are commonly altered in small-cell bladder cancer. Keratin 5 promoter-driven adenovirus Cre (Ad-K5-Cre, University of Iowa) was instilled into the bladder of female triple floxed (Trp53f/f:Pten f/f:Rb1 f/f) mice for 30 min. The mice were monitored for hematuria and bladder mass using ultrasound. Results: One Ad-K5-Cre:Trp53-/-: Pten-/-: Rb1-/- mouse died from urinary obstruction at 22 weeks. An obstructive tumor was noted in bladder trigone. Immunohistochemistry analysis of bladder tumor demonstrated negative cytokeratin 7 (CK7) expression and strong synaptophysin expression. Disseminated metastatic foci in lung were noted with positive synaptophysin expression as of primary tumor in the bladder. PCR demonstrated Cre mediated recombined alleles of the Trp53, Pten, and Rb1 in the tumor DNA but not in the tail DNA. The bladder tumor was dissociated to generate an organoid line. The organoid after 5 passages was tested for drug response of standard chemotherapy regimens. IC50 of cisplatin, etoposide, and gemcitabine were 3.1 μM, 0.8 μM, and 92.3 nM, respectively. Further characterization of more mice will address the limitation of small sample size. Conclusion: Inactivation of Trp53, Pten, and Rb1 is sufficient to induce metastatic small-cell carcinoma of bladder. This mouse model provides a powerful tool to study molecular mechanism of neuroendocrine differentiation and screen novel therapeutic drugs for small-cell carcinoma of bladder. Citation Format: Dongbo Xu, Qiang Cao, Li Wang, Yanqing Wang, Xiaojing Zhang, Yue Wu, Gary Smith, Bo Xu, David Goodrich, Qiang Li. A novel mouse model for small-cell carcinoma of bladder [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr B13.