Role of long noncoding RNA H19 in driving enzalutamide resistant neuroendocrine prostate cancer

INTRODUCTION: Approximately one-fourth of the prostate cancer (PCa) patients relapsing androgen deprivation therapy (ADT) have been shown to develop neuroendocrine prostate cancer (NEPC). One of the primary mechanisms attributed to this resistance is the lineage switching of epithelial cells to neuroendocrine (NE) phenotype making them independent of androgen receptor (AR) pathways for survival. Molecular basis essential to this lineage switch requires further elucidation. Thus, we aim to understand key mechanistic pathways that drive the development and maintenance of NEPC, and to investigate if the inhibition of pathway can re-sensitize to ADT in NEPC. METHODS: Bioinformatics analysis was performed with existing databases to compare prostate adenocarcinoma (PCA) vs NEPC. Molecular features of NEPC have been shown to depict RB1 loss in 70-90% and TP53 loss in 56-67% of the cases. Thus, we established prostate organoid cultures from P53 fl/fl /Rb fl/fl mouse and infected them with Cre-lentivirus for combined loss of TP53/Rb1. Various PCA and NEPC cell lines and patient derived organoids were used to study the role of the long non-coding RNA H19 in NEPC. Organoid growth were assessed with Incucyte and invasive capacity was measured by Matrigel invasion assay. RESULTS: Bioinformatic analysis of exisiting human PCa data sets demonstrate that H19 is one of the most highly expressed genes in NEPC and parallels the expression of NE markers. Indeed, we confirmed that H19 expression was high in various NEPC cell lines and NE patient derived organoids. H19 was also found to be markedly induced in mouse prostate organoids and LNCaP cells after TP53/Rb1 loss. Importantly, overexpression of H19 induced NE genes while suppressing the genes involved in AR signaling in LNCaP and primary PCa patient derived organoids and inversely, knockdown (KD) of H19 in LNCaP and mouse prostate organoids with TP53/Rb1 loss reduced the expression of NE gene. Interestingly, the KD of H19 in these cells re-induced the luminal phenotype, consequently restoring their sensitivity to ADT. These findings strongly implicate H19 in driving the NE lineage switch. The KD of H19 in these organoids led to a regression of tumor growth and invasiveness, suggesting H19 is required in malignant states. H19 KD decreases stem cell genes (SOX2, OCT4) via methylation of their promoters, and levels of EZH2, which methylates 9Lys-99 (H3K9me) and 9Lys-279 (H3K27me) of histone H3 and represses transcription of the target genes. H3K27me3 levels, which are high in NEPC, was reduced in the H19 KD, suggesting H19 works in an epigenetic regulation to induce NEPC phenotype. CONCLUSION: These data highlight H19 as a novel regulator in controlling the lineage switch to NEPC, tumor growth, and the sensitivity to hormone blockade, suggesting that H19 regulation will be important for developing treatments specifically aimed for this highly aggressive form of prostate cancer. Citation Format: Neha Singh, Virginie Olive, Ritu Pandey, Jin Song, Jeremiah Bearrs, Sathish K. Padi, Koichi Okumura, Andrew S. Kraft. Role of long noncoding RNA H19 in driving enzalutamide resistant neuroendocrine prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3017.