Abstract 3017: Identifying drivers for advanced prostate cancer by a transposon-based genetic screen
Authors: Zou Min , Vasciaveo Alessandro , Califano Andrea , Abate-Shen Cory 
Published: August 2018

Abstract
Prostate cancer remains the second leading cause of cancer death in men in the United States. Androgen-deprivation therapy (ADT) often leads to progression to castration-resistant prostate cancer (CRPC), which is more aggressive and frequently associated with metastasis and poor prognosis. Despite the significance of CRPC in the clinic, the molecular mechanism driving the emergence of advanced prostate cancer is still not well understood. Identifying novel drivers is particularly important for developing therapeutic targets that lead to improved treatment outcome. We sought to explore drivers for advanced prostate cancer by utilizing the Sleeping Beauty (SB) system, a murine transposition-based forward mutagenesis screening approach. We generated mouse strain in which the SB transposase expression is under the control of a tamoxifen-inducible Cre allele driven by the prostate specific Nkx3.1 promoter. After crossing this strain to transgenic strain for the transposon element (T2/Onc2), as well as strain with floxed alleles for Pten and Trp53, we obtained a mouse model allowing mutagenesis screening in mouse prostate on a Pten and Trp53 null background (SB mice). Mice with only conditional deletion of Pten and Trp53 were generated as controls. Prostate tumor tissue from moribund mice were collected for sequencing and histopathologic analysis. Kaplan-Meier survival analysis was performed to examine the disease progression. Linker-mediated PCR was performed to amplify genomic loci containing SB transposon insertions. Barcoded sequencing library was generated and sequenced on an Illumina HiSeq4000. Sequencing reads and common insertion sites (CIS) were analyzed by published TAPDANCE pipeline. Survival analysis revealed that the SB mice (n=28) have a significantly shorter time to death than the controls (n=65) (log-rank p&lt;0.0001). Interestingly, histologic analysis revealed frequent detection (11/28) of features associated with human neuroendocrine prostate cancer (NEPC), including presence of small round cells with prominent nuclei and scant cytoplasm that stain positively for neuroendocrine markers such as synaptophysin, but negatively for androgen receptor. Frequent detection of NEPC features in SB mice but not in control mice (1/53) suggests that SB-mediated mutagenesis drives NEPC development. CIS analysis revealed more than 200 insertion sites with statistical significance (integrated p&lt;0.05), which require further validation in human tumors. In conclusion, we have implemented the SB genetic screen system in our existing CRPC mouse model. Our data show that SB mice present with accelerated disease progression and higher incidence of NEPC tumor features, consistent with a lethal and aggressive subtype of human CRPC. CIS analysis have identified hundreds of insertion sites, which are likely to include novel candidate drivers of aggressive prostate cancer.
Citation Format: Min Zou, Alessandro Vasciaveo, Andrea Califano, Cory Abate-Shen. Identifying drivers for advanced prostate cancer by a transposon-based genetic screen [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3017.