Poster Session #1 PS1-01 A negative feedback loop of vitamin D import into African American prostate cells and tissues may have implications in hormonal carcinogenesis contributing to prostate cancer disparities. J Garcia1, Z Richards2, L Nonn1 University of Illinois at Chicago1; Dana-Farber Cancer Institute, Harvard Medical School2 Introduction & Objective : Prostate cancer (PCa) is a hormonally driven cancer and is currently the third most common cancer in the US. African American (AA) men are disproportionately at risk for both PCa and vitamin D (vitD) deficiency compared to white men. The numerous chemopreventative properties of vitD and epidemiological relationship of vitD status with PCa aggressiveness and mortality has led to the hypothesis that vitD deficiency is a biological contributor to the PCa disparity in AA men. Methods : Here we examine the mechanisms that regulate hormone import into the prostate to follow-up on unexpected relationships between serum and intraprostatic vitD metabolites in AA men that our lab recently reported. Results : We also found that Megalin, a multi-liganded endocytic membrane receptor encoded by the gene LRP2, is present on prostate epithelium and is regulated by vitD. Extra-renal activity of Megalin has not been well studied as the widely accepted Free Hormone Hypothesis assumes passive diffusion of circulating free hormones into tissues. However, the presence of megalin suggests that globulin bound hormones from the circulation, including 25D bound to vitamin D binding protein (DBP) and testosterone (T) bound to sex hormone binding globulin (SHBG), are imported into prostate in a regulated manner. Moreover, we found similar relationships between serum and intraprostatic testosterone metabolites, further supporting active megalin; AA men had higher levels of dihydrotestosterone (DHT) in prostate tissue compared to white men. Examination of megalin in vitro in primary human prostate cells and in tissue explants demonstrated that globulin-bound hormones are imported into the prostate and transcriptionally active. In vitro 25D deficiency increased expression of megalin protein and LRP2 expression in cells and tissue slices. 25D decreased LRP2 promoter activity in prostate cells. We also observed megalin-mediated internalization of DBP-bound 25D and SHBG-bound T into prostate cells. Ongoing studies are examining megalin-mediated import of estrogens, which are also implicated in carcinogenesis. Conclusions : In summary our findings support the presence of a negative feedback loop in which vitD deficiency increases hormone import into prostate epithelium via Megalin. Therefore the upregulation of megalin in the setting of vitamin D deficiency may facilitate increased import of circulating sex steroids into the prostate contributing to carcinogenesis in AA men. PS1-02 Bladder Cancer Rapid Autopsy: Emerging patient-derived xenograft models for metastatic diseases H Lam1, F Vakar-Lopez, H Cheng1, M Schweizer1, P Grivas2, EY Yu1, B Montgomery1, A Hsieh3, E Corey4, J Wright University of Washington1; University of Washington/Seattle Cancer Care Alliance2; Fred Hutchinson Cancer Research Center3; University of Washington School of Medicine4 Introduction & Objective : Patients with metastatic bladder cancer have a poor prognosis with a median survival of only 9-15 months. Understanding the biology of metastatic bladder cancer has been historically difficult due to a paucity of specimens and models that recapitulate human disease. To date, xenograft models of bladder cancer have been restricted to cell line or primary bladder cancer, models reflecting metastatic disease were not available. To this end, we established a bladder cancer rapid autopsy program to systemically acquire bladder cancer metastases, and build patient-derived xenograft (PDX) and organoid models for biological studies. Methods : Patients with metastatic bladder cancer were consented and a rapid autopsy was performed 2-6 hours after death to allow acquisition of normal and metastasis specimens. Frozen and formalin-fixed and paraffin embedded specimens were deposited into our biorepository and pathological evaluation was performed on each specimen. Additionally, tumors were implanted subcutaneously into SCID mice to establish PDXs. Once PDXs were developed, PDXs were dissociated for companion organoid culture. Clinical history and treatment information was documented for each participant. Results : We have performed 12 bladder cancer rapid autopsies to date, and have acquired 110 metastatic and 55 normal specimens. The pathological subtypes of these patients include urothelial cell carcinoma (4/12), and urothelial carcinoma with squamous differentiation (4/12) and plasmacytoid variant (4/12). The cohort has been treated BCG only (1/12), chemotherapy (5/12), and chemotherapy and immune checkpoint inhibitors (6/12). The leading site of metastasis was the liver (7/12) and lung (7/12), followed by lymph node (5/12), bone (5/12), intestine (4/12), and omentum (2/12). Approximately half (5/12) of the patients had extensive liver metastases that allow acquisition of multiple tumor foci. For the first time, PDX and organoids from three metastases (liver – CoCaB 10, omentum – CoCaB 14.1, liver – CoCaB 14.2) from the same patient were successfully developed for therapeutic studies. Conclusions : This bladder cancer rapid autopsy program provides an important volume of metastatic tumor specimens for study. Importantly, the first bladder cancer PDX derived from metastasis has been developed. The availability of metastatic bladder cancer specimens, PDXs, and organoids will allow biological studies of bladder cancer metastasis, heterogeneity, and treatment resistance. PS1-03 Carcinogen-induced bladder cancer in the FVB mouse strain is associated with glandular differentiation and increased Cd274/Pdl-1 expression L Shuman1, V Osei Amponsa, J Ellis1, E Wang1, V Walter1, M Zaleski2, J Warrick, JD Raman1, D DeGraff1 Penn State College of Medicine1; Penn State Health. MS Hershey Medical Center2 Introduction & Objective : Creation of genetically engineered mouse models of bladder cancer often involves the use of several background strains in conjunction with the carcinogen N-butyl-N- (4-hydroxybutyl) nitrosamine (BBN). However, carcinogen susceptibility in commonly used strains, as well as phenotypic differences, is not well characterized. Therefore, the objective of this study is to determine differences in susceptibility and phenotypic outcome following BBN exposure of C57BL/6 and FVB mice, two strains commonly used for model development. Methods : Male C57BL/6 and FVB mice were exposed to BBN (0.05%) in drinking water for 12 and 16 weeks. Dissected bladders were characterized by histological and immunohistochemical analyses. In addition, Gene Ontology analysis was performed to identify differences in gene expression across strains following BBN exposure. Results : While the C57BL/6 strain developed non-invasive (<pT1) tumors following 12 and 16 weeks of BBN exposure, FVB mice developed muscle invasive bladder cancer with squamous and/or glandular differentiation. Interestingly, glandular differentiation was exclusively observed in the FVB strain. FVB tumors were also highly immunogenic and inflamed as indicated by high expression of Cd274 (Pdl-1), murine histocompatibility complex (H2), and pro- inflammatory cytokines (Il-5 and Il-17). Conclusions : Following BBN exposure, FVB mice undergo rapid tumorigenesis and disease progression characterized by Pdl-1 expression and development of glandular differentiation. These studies identify a degree of tumor heterogeneity in the FVB tumors previously undescribed, and identify FVB mice as a potentially useful model for the study of bladder adenocarcinoma and the inflammatory tumor microenvironment. PS1-04 Characterization of Srd5a2creErt2 Expression in the Mouse Prostate: A Potential Source of Stromal Progenitors K Wegner, J Guo, J McMahon, A McMahon, CM Vezina University of Wisconsin-Madison Introduction & Objective : Many genetic tools are available for studying prostate epithelial cells in mice, but surprisingly few have been validated for prostate stroma. The lack of genetic mouse lines targeting prostate stroma has made identification of potential stromal progenitors difficult. Pinpointing these progenitors is the first step in identifying mechanisms responsible for stromal disease causing behaviors, including proliferation, growth factor release, and extracellular matrix synthesis. Methods : This study uses the Srd5a2creErt2mouse strain which expresses cre recombinase driven by the steroid 5 alpha-reductase type 2 (Srd5a2) promoter. Six-week-old male mice received four daily 200mg/kg doses of tamoxifen to activate cre. We mapped cre expression in adult male Srd5a2creErt2 mice using a fluorescent reporter mouse strain (tdTomatofl). To examine the regenerative capacity of these cells, mice were castrated seven days after cre activation, and subcutaneous testosterone (T) capsules were implanted two weeks later. T capsules were then removed and replaced at regular intervals a total of three times. To genetically ablate SRD5A2-expressing cells, Srd5a2creErt2 mice were crossed to mice which, upon cre- mediated recombination, express diphtheria toxin A subunit (DTA). Results : Fluorescent reporter experiments reveal that Srd5a2creErt2 is highly expressed in all prostate lobes and to a lesser degree in the seminal vesicle and testis. Cells expressing cre are largely localized to the fibromuscular tunica