Abstract 436: An orthotopic murine model of neuroendocrine bladder cancer offers insights into the phenotypic plasticity of small cell bladder cancer (SCBC)
Authors: Balyimez Aysegul , Ganguly Shinjini , Thirunavukkarasu Sitalaximi , Grivas Petros , Ornstein Moshe , Gupta Shilpa , Lee Byron , McFarland Chris , Winslow Monte , McKenney Jesse , Mian Omar Y. 
Published: September 2020

Abstract
Purpose: SCBC is an aggressive subtype of bladder cancer with high metastatic potential and few effective treatment options. We developed the first orthotopic murine model of SCBC to study the development of this aggressive variant, identify epigenetic drivers of urothelial transdifferentiation, and explore novel therapeutic approaches.
Methods: Lentiviral particles designed to transduce Cre recombinase gene were produced (Lenti-sgNeo#2/Cre). High titer virus was prepared and confirmed using a fluorescent Cre reporter assay. Transurethral catheterization of the bladder was performed using Rb1fl/fl Trp53fl/fl MycLSL/LSL (RPM) mice and 30 minute lentivirus instillations were conducted under anesthesia. Mice were monitored by micro-ultrasound (mUS) and tumor bearing mice were sacrificed, examined for metastases, and tissues were harvested for analysis by a genitourinary pathologist. SCBC / high grade neuroendocrine histology was confirmed by H&E and synaptophysin IHC. Whole transcriptome (RNAseq) analysis was performed to correlate transcriptomic profile of neuroendocrine mouse tumors to a cohort of human SCBC tumors.
Results: Transurethral catheterization was successfully performed in RPM mice (n=10); the bladder urothelium was transduced without evidence of exposure to ectopic (non-urothelial) tissues. RPM mice developed SCBC visible on mUS with a latency of 8-10 weeks. 4/10 mice had liver or lung metastases grossly or had microscopic metastatic deposits upon analysis of tissues. High grade neuroendocrine morphology and NE marker expression were confirmed by H&E and IHC, respectively, in all harvested tumors. Western blot analysis confirmed cMyc expression and suppression of TP53 and RB1. Synaptophysin expression was confirmed by IHC. Transcriptomic profiling of mouse and human SCBC demonstrated largely concordant gene expression (R2=0.47) and upregulation of neuroendocrine genes.
Conclusions: To our knowledge, this is the first genetically engineered orthotopic murine model of SCBC. Current work seeks to identify reversible epigenetic drivers of neuroendocrine transdifferentiation and novel therapeutic targets in this aggressive variant of bladder cancer. In addition, we are assessing the activity of immune checkpoint inhibitors in this immunocompetent model.
Citation Format: Aysegul Balyimez, Shinjini Ganguly, Sitalaximi Thirunavukkarasu, Petros Grivas, Moshe Ornstein, Shilpa Gupta, Byron Lee, Chris McFarland, Monte Winslow, Jesse McKenney, Omar Y. Mian. An orthotopic murine model of neuroendocrine bladder cancer offers insights into the phenotypic plasticity of small cell bladder cancer (SCBC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 436.