Abstract LB247: A forward genetic screen to identify drivers of neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is a deadly variant of prostate cancer for which no cure is yet available. Up to 20 percent of the patients with castration resistant prostate cancer (CRPC), will progress to NEPC after treatment with standard-of-care therapies, such as abiraterone and enzalutamide, that target the androgen receptor (AR) pathway. However, the molecular mechanisms that drive the emergence of NEPC are largely unknown, contributing to a lack of treatment options for patients with NEPC. We implemented a forward genetic approach to identify novel drivers of NEPC, by using the Sleeping Beauty (SB) transposon-based forward genetic mutagenesis screening system in our Pten-, Trp53-deficient mouse model that is primed to develop NEPC at a low frequency. We generated a mouse strain (NPp53SBT2Onc) in which the Nkx3.1 promoter regulates the expression of tamoxifen-inducible Cre specifically in the mouse prostate epithelium, resulting in transposition of the T2Onc2 transposable element and conditional deletion of Pten and Trp53 in mouse prostate epithelium. We observed an increased NEPC incidence in our NPp53SBT2Onc mouse model compared to control mice without the transposon T2Onc2, suggesting that the SB-mediated insertional mutagenesis events are driving the development of NEPC. To elucidate the genetic events that are driving the observed NEPC phenotype, we identified the common insertion sites (CISs) of the transposon insertions, which revealed a total of 330 CIS-associated genes. We further performed an integrative analysis using RNA-seq data from our SB cohort, a second mouse dataset and a metastatic CRPC patient cohort, which allowed us to identify the Master Regulator (MR) proteins that are associated with NEPC, as well as the upstream genomic events that modulate these MRs and the emergence of NEPC. Altogether, our approach resulted in the identification of CIS-associated genes that are upstream of these MRs associated to NEPC and that are likely to drive this lethal subtype of prostate cancer. We will further validate and elucidate the role of these candidate genes in prostate cancer progression to NEPC, in both mouse and human using CRISPR technology. In summary, we have developed a Sleeping Beauty forward genetic screen in our mouse model of CRPC, which not only accelerates disease progression, but also increases the incidence of NEPC. Our integrative analysis identified a panel of CIS-associated genes that are likely to be functionally involved in progression to NEPC. Validation of candidate drivers resulting from our analysis will shed light on mechanisms that this aggressive disease uses to evade treatments and may inform the development of novel therapies. Citation Format: Francisca Nunes de Almeida, Alessandro Vasciaveo, Min Zou, Matteo Di Bernardo, Andrea Califano, Cory Abate-Shen. A forward genetic screen to identify drivers of neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB247.