Abstract 4327: Hypermethylation of miR193b reactivates master drivers of the poor prognosis prostate cancer

Epigenetic silencing of miRNAs is one of the major mechanisms of aberrant miRNA expression in cancer. Several studies showed that hypermethylation of miRNAs contributes to prostate cancer (PC) initiation and progression. Recent screening for epigenetically regulated miRNAs in PC revealed hypermethylation of the miR-193b in tumor, but no related functional studies of miR-193b have been pursued. miR-193b functions as a tumor suppressor in various cancer by targeting multiple oncogenic pathways. Methylation regulated miR-193b silencing has been observed in multiple cancer types. In this study, we aimed to elucidate the function of miR-193b and related molecular mechanisms in PC. In TCGA cohort, we observed a significant correlation between methylation of the miR-193b and its expression level. We further confirmed that some of PC cell lines recapitulate the methylation of miR-193b seen in clinical samples. The phenotypes induced by exogenous miR-193b in PC cell lines showed the tumor suppressive property of miR-193b. Since some of miRNA-target interactions are conserved across organisms, we selected the top 150-downregulated genes by miR-193b in liposarcoma from public available datasets and unraveled the correlation between these genes with PC progression. We further applied the 150 genes to the PC subtype (PCS) signatures. There were 41 genes overlapping with the aggressive PCS1 among 150 genes, indicating miR-193b may affect these key 41 genes that regulate PC progression. The inhibition of the 41 genes by miR-193b was validated in multiple PC cell lines. Furthermore, high expression of these genes was highly correlated with recurrence of PC. The GSEA analysis of 41 genes revealed high enrichment in the FOXM1 target network. We further identified FOXM1 as a direct target of miR-193b and overexpression of FOXM1 is highly correlated with clinical outcomes including metastasis and lethality. Besides FOXM1, we also identified RRM2 as another important target of miR-193b, which is part of the PCS1 signature. Knockdown of RRM2 phenocopied miR-193b in PC cells. Its overexpression is highly correlated clinical outcomes. To explore the therapeutic potential of regulating miR-193b levels, we restored miR-193b expression by using combination treatment with DNMT and HDAC inhibitors (5-azacytidine and mocetinostat), resulting in the inhibition of FOXM1 and RRM2 expression. Interestingly, FOXM1 and RRM2 expression are highly correlated in multiple PC cohorts. All together, we revealed the tumor suppressive function of miR-193b in PC. A 41-gene set was identified and validated as the targets of miR-193b in PC cells, and showed a high correlation with PC progression in multiple PC cohorts. FOXM1 and RRM2 may be the key targets of miR-193b in PC. Our findings suggest that hypermethylation of miR-193b in PC may release the inhibition of some key oncogenes that contribute PC progression. Citation Format: Ying Z. Mazzu, Yuki Yoshikawa, Subhiksha Nandakumar, Joshua Armenia, Lina Jehane, Gwo-Shu Lee, Goutam Chakraborty, Philp Kantoff. Hypermethylation of miR193b reactivates master drivers of the poor prognosis 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 4327.