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Endocrine therapies for prostate cancer inhibit the androgen receptor (AR) transcription factor. In most cases, AR activity resumes during therapy and drives progression to castration-resistant prostate cancer (CRPC). However, therapy can also promote lineage plasticity and select for AR-independent phenotypes that are uniformly lethal. Here, we demonstrate the stem cell transcription factor Krüppel-like factor 5 (KLF5) is low or absent in prostate cancers prior to endocrine therapy, but induced in a subset of CRPC, including CRPC displaying lineage plasticity. KLF5 and AR physically interact on chromatin and drive opposing transcriptional programs, with KLF5 promoting cellular migration, anchorage-independent growth, and basal epithelial cell phenotypes. We identify ERBB2 as a point of transcriptional convergence displaying activation by KLF5 and repression by AR. ERBB2 inhibitors preferentially block KLF5-driven oncogenic phenotypes. These findings implicate KLF5 as an oncogene that can be upregulated in CRPC to oppose AR activities and promote lineage plasticity., While many treatments for prostate cancer suppress the androgen receptor it becomes reactivated during disease progression. Here, the authors show that a KLF5 transcriptional programme is also activated during treatment and promotes migration and the appearance of a basal cell phenotype.

Despite recent therapeutic advances, prostate cancer remains a leading cause of cancer-related death. A subset of castration-resistant prostate cancers become androgen receptor (AR) signaling independent and develop neuroendocrine prostate cancer (NEPC) features through lineage plasticity. These NEPC tumors, associated with aggressive disease and poor prognosis, are driven, in part, by aberrant expression of N-Myc, through mechanisms that remain unclear. Integrative analysis of the N-Myc transcriptome, cistrome, and interactome using in vivo, in vitro, and ex vivo models (including patient-derived organoids) identified a lineage switch towards a neural identity associated with epigenetic reprogramming. N-Myc and known AR cofactors (e.g., FOXA1 and HOXB13) overlapped, independently of AR, at genomic loci implicated in neural lineage specification. Moreover, histone marks specifically associated with lineage-defining genes were reprogrammed by N-Myc. We also demonstrated that the N-Myc–induced molecular program accurately classifies our cohort of patients with advanced prostate cancer. Finally, we revealed the potential for enhancer of zeste homolog 2 (EZH2) inhibition to reverse the N-Myc–induced suppression of epithelial lineage genes. Altogether, our data provide insights into how N-Myc regulates lineage plasticity and epigenetic reprogramming associated with lineage specification. The N-Myc signature we defined could also help predict the evolution of prostate cancer and thus better guide the choice of future therapeutic strategies.

In castration-resistant prostate cancer (CRPC), the loss of androgen receptor (AR)-dependence due to lineage plasticity, which has become more prevalent, leads to clinically highly aggressive tumors with few therapeutic options and is mechanistically poorly defined. To identify the master transcription factors (TFs) of CRPC in a subtype-specific manner, we derived and collected 29 metastatic human prostate cancer organoids and cell lines, and generated ATAC-seq, RNA-seq and DNA sequencing data. We identified four subtypes and their master TFs using novel computational algorithms: AR-dependent; Wnt-dependent, driven by TCF; neuroendocrine, driven by ASCL1 and NEUROD1 and stem cell-like (SCL), driven by the AP-1 family. The transcriptomic signatures of these four subtypes enabled the classification of 370 patients. We find that AP-1 co-operates with the inhibitable YAP/TAZ/TEAD pathway in the SCL subtype, the second most common group of CRPC tumors after AR-dependent. Together, this molecular classification reveals new drug targets and can potentially guide therapeutic decisions.

Following treatment with androgen receptor (AR) pathway inhibitors, ~20% of prostate cancer patients progress by shedding their dependence on AR. These tumors undergo epigenetic reprogramming turning castration-resistant prostate cancer adenocarcinoma (CRPC-Adeno) into neuroendocrine prostate cancer (CRPC-NEPC). Currently, no targeted therapies are available for CRPC-NEPCs. A major hurdle in the development of new therapies and treatment of CRPC-NEPC is the lack of accurate models to test candidate treatments. Such models would ideally capture components of the tumor microenvironment (TME) factors, which likely regulate the phenotypic, genetic, and epigenetic underpinnings of this aggressive subset. The TME is a complex system comprised not only of malignant prostate cells but also stromal and inflammatory cells and a scaffold of extracellular matrix (ECM). ECM proteins are implicated in the survival and progression of cancer and development of chemoresistance, while are equally integral to the development of prostate cancer organoids. Here, using a combination of patient tumor proteomics and RNA sequencing, we define putative ECM cues that may guide the growth of prostate tumors in patients. Using this molecular information, we developed synthetic hydrogels that recapitulate the tumor ECM. Organoids cultured in the synthetic hydrogel niches demonstrate that ECM subtypes regulate the morphology, transcriptome, and epigenetics hallmarks of CRPC-Adeno and CRPC-NEPC. CRPC-NEPC organoid showed a differential response to small molecule inhibitors of epigenetic repressor EZH2 and Dopamine Receptor D2 (DRD2), the latter being a novel target in CRPC-NEPC when grown in tumor-specific ECM. Finally, in those synthetic ECM niches where drug resistance was observed in CRPC-NEPCs, cellular reprogramming by a synergistic combination of EZH2 inhibitors with DRD2 antagonists inhibited tumor growth. The synthetic platform can provide a more realistic prostate-specific microenvironment and subsequently enable the development of effective targeted therapeutics for prostate cancers.

Although a de novo clinical presentation of small cell neuroendocrine carcinoma of the prostate is rare, a subset of patients previously diagnosed with prostate adenocarcinoma may develop neuroendocrine features in later stages of castration-resistant prostate cancer (CRPC) progression as a result of treatment resistance. Despite sharing clinical, histologic, and some molecular features with other neuroendocrine carcinomas, including small cell lung cancer, castration-resistant neuroendocrine prostate cancer (CRPC-NE) is clonally derived from prostate adenocarcinoma. CRPC-NE therefore retains early prostate cancer genomic alterations and acquires new molecular changes making them resistant to traditional CRPC therapies. This review focuses on recent advances in our understanding of CRPC-NE biology, the transdifferentiation/plasticity process, and development and characterization of relevant CRPC-NE preclinical models.

Purpose: Neuroendocrine prostate cancer (NEPC) is an aggressive variant of prostate cancer that may develop de novo or as a mechanism of treatment resistance. N-myc is capable of driving NEPC progression. Alisertib inhibits the interaction between N-myc and its stabilizing factor Aurora-A, inhibiting N-myc signaling, and suppressing tumor growth. Patients and Methods: Sixty men were treated with alisertib 50 mg twice daily for 7 days every 21 days. Eligibility included metastatic prostate cancer and at least one: small-cell neuroendocrine morphology; ≥50% neuroendocrine marker expression; new liver metastases without PSA progression; or elevated serum neuroendocrine markers. The primary endpoint was 6-month radiographic progression-free survival (rPFS). Pretreatment biopsies were evaluated by whole exome and RNA-seq and patient-derived organoids were developed. Results: Median PSA was 1.13 ng/mL (0.01–514.2), number of prior therapies was 3, and 68% had visceral metastases. Genomic alterations involved RB1 (55%), TP53 (46%), PTEN (29%), BRCA2 (29%), and AR (27%), and there was a range of androgen receptor signaling and NEPC marker expression. Six-month rPFS was 13.4% and median overall survival was 9.5 months (7.3–13). Exceptional responders were identified, including complete resolution of liver metastases and prolonged stable disease, with tumors suggestive of N-myc and Aurora-A overactivity. Patient organoids exhibited concordant responses to alisertib and allowed for the dynamic testing of Aurora–N-myc complex disruption. Conclusions: Although the study did not meet its primary endpoint, a subset of patients with advanced prostate cancer and molecular features supporting Aurora-A and N-myc activation achieved significant clinical benefit from single-agent alisertib.

Castration-resistant prostate cancer (CRPC) is a heterogeneous disease with diverse drivers and mechanisms of resistance to androgen receptor (AR) therapy. We generated ATAC-seq and RNA-seq data for twenty-four metastatic human prostate cancer organoids and cell lines. Integration of chromatin accessibility profiles and transcriptomes revealed four subtypes: androgen-receptor(AR)-dependent, neuroendocrine, Wnt-dependent and epithelial mesenchymal transition (EMT). The transcriptomic signatures obtained from these four subtypes enable the classification of 100 metastatic prostate cancer patient samples from Institute Precision Medicine (IPM) and 270 published samples from SU2C study, revealing potential therapeutic vulnerabilities. Furthermore, using novel computational algorithms we constructed regulatory networks and identified the master regulators of each subtype. Currently we're carrying out western blot and quantitative PCR to confirm the subtypes of all prostate cancer models we use, and using drug sensitivity test, CRISPR knockout and cell competition assay to validate the functions of candidates in each subtype. Our study has characterized global chromatin accessibility landscape and transcriptome in the largest number of metastatic prostate cancer models, which revealed novel subtypes and corresponding tumor drivers. Collectively, these organoids, cell lines and matching sequence data provide a resource to the community to study various CRPC models. The molecular classification and corresponding master regulators reveal new drug targets and could potentially guide future therapeutic studies. Citation Format: Fanying Tang, Chen Khuan Wong, Sandra Cohen, Cindy Lee, Minwei Liu, Rohan Bareja, Kenneth Eng, Shaham Beg, Loredana Puca, Cora Sternberg, Juan Miguel Mosquera, Himisha Beltran, Andrea Sboner, Yu Chen, Ekta Khurana. Chromatin accessibility landscape and transcriptome of castration resistant prostate cancers reveals novel subtypes and diverse master regulators [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 5310.

Loss of androgen receptor (AR) signaling dependence occurs in approximately 15-20% of treatment resistant prostate cancers, and this may manifest clinically as transformation from a prostate adenocarcinoma histology to a castration resistant neuroendocrine prostate cancer (CRPC-NE). The diagnosis of CRPC-NE currently relies on a metastatic tumor biopsy, which is invasive for patients and often challenging to diagnose due to tumor heterogeneity. By studying whole exome sequencing and whole genome bisulfite sequencing of metastatic tumor biopsies and matched cell free DNA (cfDNA), we identified distinct genomic and epigenomic features of CRPC-NE and patterns of tumor evolution that occur during clinical progression and treatment resistance. Loss of RB1 and TP53 are enriched in CRPC-NE compared with castration resistant prostate adenocarcinoma, as are significant changes in DNA methylation, which are detectable by cfDNA. There was significantly higher concordance between cfDNA and biopsy tissue genomic alterations in CRPC-NE patients compared to castration resistant adenocarcinoma, supporting greater intra-individual genomic consistency across metastases. cfDNA and serial tumor biopsies allowed for the tracking of dynamic clonal and subclonal tumor cell populations as patients progressed and identified CRPC-NE alterations sometimes prior to the development of clinical features. CRPC-NE appears to arise clonally from a prostate adenocarcinoma precursor likely through a dynamic process of clonal selection and trans-differentiation that occurs during resistance to AR-directed therapies. In addition to loss of AR expression and canonical AR signaling, we identified a dysregulation of key pathways in CRPC-NE including loss of Notch signaling, reactivation of developmental programs, and gain of neuronal/neuroendocrine programs including critical lineage determining transcription factors (LDTFs) such as ASCL1, MYCN, BRN2, pointing to novel biomarkers and potential targets for CRPC-NE. Patient-derived organoids and xenografts were used to interrogate the timing by which genomic and epigenomic changes and LDTFs contribute to lineage plasticity and the development of CRPC-NE as a resistance mechanism in prostate cancer. Citation Format: Himisha Beltran, Sheng-Yu Ku, Vincenza Conteduca, Alessandro Romanel, Loredana Puca, Michael Sigouros, Juan Miguel Mosquera, Scott T. Tagawa, Andrea Sboner, Olivier Elemento, David Goodrich, David Rickman, Amina Zoubeidi, Francesca Demichelis. Lineage plasticity and the neuroendocrine phenotype as a resistance mechanism in prostate cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr CN06-01. doi:10.1158/1535-7163.TARG-19-CN06-01

For many years, β-arrestins have been known to be involved in G-protein-coupled receptor (GPCR) desensitization. However, β-arrestins belong to a family of proteins that act as multifunctional scaffolding proteins, in particular during trafficking of transmembrane receptors. The arrestin family comprises visual arrestins, β-arrestins and α-arrestins. In mammals, the functions of the α-arrestins are beginning to be elucidated, and they are described as versatile adaptors that link GPCRs or the Notch receptor to E3 ubiquitin ligases and endocytic factors. These α-arrestins can act in sequence, complementarily or cooperatively with β-arrestins in trafficking and ubiquitylation events. This Commentary will summarize the recent advances in our understanding of the functions and properties of these α-arrestin proteins in comparison to β-arrestins, and will highlight a new hypothesis linking their functional complementarity to their physical interactions. α- and β-arrestins could form transient and versatile heterodimers that form a bridge between cargo and E3 ubiquitin ligases, thus allowing trafficking to proceed.

Summary Notch signaling is a conserved signaling pathway implicated in embryogenesis and adult tissue maintenance. Notch signaling strength is strictly regulated, notably by maintaining a controlled pool of functional receptor at the cell surface. Mammalian non-activated Notch receptor is internalized, ubiquitylated by the Itch E3 ubiquitin ligase and degraded in the lysosomes. Here, we show that β-arrestins are necessary for Itch–Notch interaction and for Itch-driven ubiquitylation and degradation of Notch. Interestingly, β-arrestins do not directly bind Itch but heterodimerize with a member of another subfamily of arrestins called ARRDC1 or α-arrestin 1, which harbors PPxY motifs that allow direct interaction with Itch. Cells transfected with ARRDC1 mutated in PPxY motifs show reduced Itch-mediated Notch ubiquitylation and impaired lysosomal degradation of Notch, as observed in β-arrestin−/− or Itch−/− cells. Our data show for the first time that ARRDC1 and β-arrestins heterodimerize and cooperate in the same complex to promote non-activated Notch receptor degradation, thus acting as negative regulators of Notch signaling.

An increasingly recognized resistance mechanism to androgen receptor (AR)-directed therapy in prostate cancer involves epithelial plasticity, in which tumor cells demonstrate low to absent AR expression and often have neuroendocrine features. The etiology and molecular basis for this 'alternative' treatment-resistant cell state remain incompletely understood. Here, by analyzing whole-exome sequencing data of metastatic biopsies from patients, we observed substantial genomic overlap between castration-resistant tumors that were histologically characterized as prostate adenocarcinomas (CRPC-Adeno) and neuroendocrine prostate cancer (CRPC-NE); analysis of biopsy samples from the same individuals over time points to a model most consistent with divergent clonal evolution. Genome-wide DNA methylation analysis revealed marked epigenetic differences between CRPC-NE tumors and CRPC-Adeno, and also designated samples of CRPC-Adeno with clinical features of AR independence as CRPC-NE, suggesting that epigenetic modifiers may play a role in the induction and/or maintenance of this treatment-resistant state. This study supports the emergence of an alternative, 'AR-indifferent' cell state through divergent clonal evolution as a mechanism of treatment resistance in advanced prostate cancer.

Background: Delta-like protein 3 (DLL3) is expressed on the surface of small cell lung cancer (SCLC) tumor-initiating cells, and the DLL3 targeted antibody-drug conjugate, Rovalpituzumab tesirine (Rova-T™; SC16LD6.5), has shown promise for patients with SCLC. Neuroendocrine prostate cancer (NEPC) is an emerging late stage subtype of castration resistant prostate cancer with limited therapeutic options. Based on clinical and molecular similarities with SCLC, we investigated expression of DLL3 and the use of Rovalpituzumab tesirine in NEPC xenografts. Methods: We evaluated mRNA and/or protein expression of DLL3 in a cohort of 361 patients (552 samples) ranging from benign prostate (BEN), localized prostate adenocarcinoma (PCA), castration resistant adenocarcinoma (CRPC), and castration resistant NEPC and correlated with pathologic and genomic features. mRNA was assessed by RNAseq. Protein was assessed by immunohistochemistry (DLL3 SP347 antibody). Prostate cancer cell lines were engrafted in mice and treated with SC16LD6.5 in vivo. Results: DLL3 was expressed at the mRNA and/or protein level in 0/132 Benign (0%), 1/254 (0.4%) PCA, 10/90 (11.1%) CRPC and 47/76 (61.8%) NEPC samples. DLL3 IHC was of higher intensity in NEPC and co-localized with classical neuroendocrine (NE) markers. DLL3 was amongst the most differentially expressed genes by RNA-seq in NEPC versus CRPC (p= Conclusions: DLL3 is expressed on the surface of the majority of NEPC cases evaluated and is not expressed in primary prostate cancer or benign tissues. Modulation of DLL3 expression does not appear to affect AR or NEPC signaling in cell lines. SC16LD6.5 (Rova-T) demonstrates preferential preclinical activity in NEPC that express DLL3 compared to CRPC-adenocarcinoma that are DLL3 negative, in vivo. A Phase 1 Basket trial investigating Rova-T is now open with a dedicated NEPC arm (NCT02709889). Citation Format: Loredana Puca, Verena Sailor, Katie Gavyert, Etienne Dardenne, Kumiko Isse, Michael Sigouros, David M. Nanus, Scott T. Tagawa, Juan Miguel Mosquera, Laura Saunders, Himisha Beltran. Rovalpituzumab tesirine as a therapeutic agent for neuroendocrine prostate cancer [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 1947.

Background: The development of neuroendocrine prostate cancer (NEPC) is one mechanism of treatment resistance to androgen receptor (AR)-targeted therapies for a subset of patients with advanced prostate cancer. This is associated with transition from a prostate adenocarcinoma to small cell/NEPC histology, low AR signaling signaling, and expression of neuroendocrine markers as Chromogranin A (CGHA), Synaphophysin (SYP) and CD56). Patient derived preclinical models recapitulating the NEPC phenotype may be used to address NEPC pathogenesis and test emerging therapeutic targets. Methods: Tumor organoids were developed according to protocols previously described (Gao et al, Cell 2015). Briefly the tissue biopsies (liver and bone biopsy) were washed, enzymatically digested and then seeded in Matrigel (BD) droplets. Organoids were characterized at genomic (WES), RNA and protein level (IHC) to confirm the expression of specific markers. Lentiviral infections were performed using shRNAs against EZH2 to knock down EZH2 in organoids. Organoids were also subcutaneously injected in NSG mice to generate patient derived xenografts (PDXs) for drug treatment in vivo. Results: We developed and characterized two NEPC tumor organoids from tumor biopsies (liver and bone) of two patients both in vitro and in vivo (as PDXs). NEPC tumor organoid models retained the molecular and histological characteristic of their matched patient samples. We successfully manipulated the activity of the histone methyltransferase EZH2 by using a catalytic inhibitor and its expression by infecting organoids with shEZH2. We showed that the absence of EZH2 affects the expression of neuroendocrine-associated programs as stem cell and neuronal pathway. Moreover treatment with EZH2 inhibitor decreased tumor organoids viability and PDXs tumor volume. Drug screening approaches on NEPC organoids were used to discovery novel drug targets and combinations that could potentially benefit NEPC patients. Top single agent hits included previously identified targets such as EZH2, AURKA, as well as novel synergies. Conclusions NEPC patient tumor organoids are clinically relevant tumor models to study the NEPC phenotype in advanced prostate cancer and may be used to elucidate novel drug targets. Citation Format: Loredana Puca, Rohan Bareja, Reid Shaw, Wouter Karthaus, Dong Gao, Chantal Pauli, Juan Miguel Mosquera, Joanna Cyrta, Rachele Rosati, Rema Rao, Andrea Sboner, Carla Grandori, Giorgio Inghirami, Yu Chen, Mark A. Rubin, Himisha Beltran. Patient-derived tumor organoids of neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 992. doi:10.1158/1538-7445.AM2017-992

Akt is a serine–threonine kinase that has an important role in transducing survival signals. Akt also regulates a number of proteins involved in the apoptotic process. To find new Akt interactors, we performed a two-hybrid screening in yeast using full-length Akt cDNA as bait and a human cDNA heart library as prey. Among 200 clones obtained, two of them were identified as coding for the c-FLIPL protein. c-FLIPL is an endogenous inhibitor of death receptor-induced apoptosis through the caspase-8 pathway. Using co-immunoprecipitation experiments of either transfected or endogenous proteins, we confirmed the interaction between Akt and c-FLIPL. Furthermore, we observed that c-FLIPL overexpression interferes with Gsk3-β phosphorylation levels. Moreover, through its effects on Gsk3β, c-FLIPL overexpression in cancer cells induced resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). This effect was mediated by the regulation of p27Kip1 and caspase-3 expression. These results indicate the existence of a new mechanism of resistance to TRAIL in cancer cells, and unexpected functions of c-FLIPL.

Emerging observations from clinical trials suggest that a subset of castration resistant prostate adenocarcinomas (CRPC) eventually evolve or progress to a predominantly neuroendocrine phenotype (NEPC). This transition is emerging as an important mechanism of treatment resistance. This cell plasticity is characterized by loss of androgen receptor (AR) and prostate specific antigen (PSA), and significant over-expression and gene amplification of MYCN (encoding N-Myc). While N-Myc is a bona fide driver oncogene in several rare tumor types, the molecular mechanisms that underlie N-Myc driven NEPC have yet to be characterized. Integrating a novel genetically engineered mouse (GEM) model of prostate specific N-Myc overexpression, human prostate cancer cell line modeling, and human prostate cancer transcriptome data, we found that N-Myc over-expression leads to the development of poorly differentiated, invasive prostate cancer that is molecularly similar to human NEPC tumors. To determine if N-Myc plays a causal role in driving the NEPC phenotype, we generated GEM lines that carry a CAG-driven lox-stop-lox human MYCN gene integrated into the ROSA26 (LSL-MYCN) locus and either a Tmprss2 driven tamoxifen-activated Cre recombinase (T2-Cre) or probasin (Pb)-Cre. Since PTEN deletion is a frequent alteration in CRPC and PI3K/AKT signaling can enhance N-Myc protein stability we also engineered the mice with a floxed Pten locus. N-Myc over-expression in the context of Ptenf/+ at 3 months post-induction leads to focal mouse high-grade prostatic intraepithelial neoplasia (mHGPIN). T2-Cre; Ptenf/f; LSL-MYCN+/+ mice develop highly proliferative, diffuse mHGPIN which consists of proliferations of cells with nuclear atypia that expand the glands, imparting irregular borders and inducing a mild stromal response, mitotic figures, and incipient necrosis. RNAseq data from N-Myc these mHGPIN lesions show they are molecularly similar to NEPC based on RNAseq data from 203 human CRPC and NEPC samples. At 6 months, Pb-Cre; Ptenf/f; LSL-MYCN+/+ mice develop poorly differentiated, highly proliferative, invasive prostate cancer. Based on the RNAseq data from the N-Myc GEM line, GEM-derived mouse prostate cancer organoid cultures and isogenic cell lines, we found that N-Myc regulates a specific NEPC-associated molecular program that includes a repression of AR signaling, enhanced AKT signaling and repression of Polycomb Repressive Complex 2 target genes. We further showed that N-Myc interacts with AR and this interaction depends on Enhancer of Zeste Homolog 2 (EZH2). Finally, N-Myc expressing cell lines and organoids displayed an enhanced sensitivity to inhibitors targeting the AKT pathway, EZH2 and Aurora-A. Altogether, our data shows that N-Myc drives the neuroendocrine phenotype in prostate cancer and provides rationale for the development of new therapeutic strategies for treating this aggressive subtype of prostate cancer. Citation Format: Etienne Dardenne, Himisha Beltran, Kaitlyn Gayvert, Matteo Benelli, Adeline Berger, Loredana Puca, Joanna Cyrta, Andrea Sboner, Zohal Noorzad, Theresa MacDonald, Cynthia Cheung, Dong Gao, Yu Chen, Martin Eilers, Juan Miguel Mosquera, Brian D. Robinson, Mark A. Rubin, Olivier Elemento, Francesca Demichelis, David S. Rickman. N-Myc drives neuroendocrine prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 887.

Background and aim of the study: The mainstay of therapy for patients with metastatic prostate cancer, including castration resistant disease (CRPC), is hormonal therapy targeting the androgen receptor (AR). However, tumors ultimately develop treatment resistance, which can include epithelial plasticity associated with loss of AR expression, clinical aggressiveness, and pathologic features of small cell or neuroendocrine carcinoma (NEPC). We recently preformed integrative molecular analyses of metastatic tumors from a large cohort of CRPC and NEPC patients. Emerging data from this study points to a key role of the Polycomb gene EZH2 and the epigenome in driving this adaptive response mechanism. In this study we are now exploring the hypothesis that the epigenetic modifier, EZH2, can lead the adaptive response towards an androgen-independent phenotype and towards the appearance of neuroendocrine features. Results: Based on the driving role of EZH2 in other tumor types and significant overexpression in NEPC tumors (confirmed at a protein level on Tissue Microarray), we evaluated the effects of the EZH2 inhibitor, GSK343, in NEPC cells (NCI-H660) and prostate adenocarcinoma cells (LNCaP and DU145) in 3D Matrigel cultures. GSK343 effectively inhibited H3K27me3 and resulted in a significant reduction of NCI-H660 viability, measured with an ATP-based assay, whereas LNCaP and DU145 cells were minimally affected after 7 or 14 days of treatment. Using a nanosting assay we also demonstrated a significant increase in the expression of AR signaling genes (such as PSA, PSMA) and decrease in NEPC-associated genes (chromogranin A, AURKA, ENO2) when neuroendocrine cells are treated with EZH2 inhibitor. These data suggest a modulation of the neuroendocrine phenotype via EZH2. We therefore extended these drug studies including patient-derived organoid models including both CRPC and NEPC organoids, and we observed similar results with preferential sensitivity of the AR-negative NEPC organoids to the AR-positive CRPC organoid, with similar reversion of downstream AR/NEPC gene expression. Conclusions: There is no approved drug that can specifically target AR- independent NEPC tumors. The restricted set of therapeutic options against this subtype of prostate cancer and consequent dismal outcome stem in part from our incomplete understanding of the molecular events underlying its pathogenesis. The discovery that epigenetics can be a key process in distinguishing tumors that are AR-independent and at high risk for NEPC progression represents an important step to highlight the use of epigenetic modifiers as therapeutic agents for this subtype of prostate cancer. Citation Format: Loredana Puca, Dong Gao, Myriam Kossai, Joanna Cyrta, Clarisse Marotz, Juan Miguel Mosquera, Theresa Y. MacDonald, Andrea Sboner, Rema Rao, Yu Chen, Mark A. Rubin, Himisha Beltran. Targeting androgen-independent prostate cancer through epigenetic reprogramming. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Sep 24-27, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2016;76(2 Suppl):Abstract nr B41.

Akt is a serine threonine kinase with a major role in transducing survival signals and regulating proteins involved in apoptosis. To find new interactors of Akt involved in cell survival, we performed a two-hybrid screening in yeast using human full-length Akt c-DNA as bait and a murine c-DNA library as prey. Among the 80 clones obtained, two were identified as Bcl-w. Bcl-w is a member of the Bcl-2 family that is essential for the regulation of cellular survival, and that is up-regulated in different human tumors, such as gastric and colorectal carcinomas. Direct interaction of Bcl-w with Akt was confirmed by immunoprecipitation assays. Subsequently, we addressed the function of this interaction: by interfering with the activity or amount of Akt, we have demonstrated that Akt modulates the amount of Bcl-w protein. We have found that inhibition of Akt activity may promote apoptosis through the downregulation of Bcl-w protein and the consequential reduction in interaction of Bcl-w with pro-apoptotic members of the Bcl-2 family. Our data provide evidence that Bcl-w is a new member of the Akt pathway and that Akt may induce anti-apoptotic signals at least in part through the regulation of the amount and activity of Bcl-w.

The transition from castration-resistant prostate adenocarcinoma (CRPC) to neuroendocrine prostate cancer (NEPC) has emerged as an important mechanism of treatment resistance. NEPC is associated with overexpression and gene amplification of MYCN (encoding N-Myc). N-Myc is an established oncogene in several rare pediatric tumors, but its role in prostate cancer progression is not well established. Integrating a genetically engineered mouse model and human prostate cancer transcriptome data, we show that N-Myc overexpression leads to the development of poorly differentiated, invasive prostate cancer that is molecularly similar to human NEPC. This includes an abrogation of androgen receptor signaling and induction of Polycomb Repressive Complex 2 signaling. Altogether, our data establishes N-Myc as an oncogenic driver of NEPC.