Abstract 4760: ER-β/Sp/NFκB/FLIP axis: Potential therapeutic target in prostate cancer

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Emergence of hormone-refractory prostate cancer is fatal for lack of effective, durable systemic therapeutic strategies. Therefore, discovery of novel approaches and agents that can prevent development of therapeutically resistant disease and its progression is critical for successful management of prostate cancer (PCA). One of the reasons for the inability to implement such strategies is an incomplete understanding of molecular events associated with the development of therapeutically resistant disease. Previously, we reported the anti-tumorigenic potential of 2-methoxyestradiol (2-ME2) both in vitro and in vivo. We showed that (i) transcription factor Sp1 activates while Sp3 inhibits Sp1-mediated transactivation of anti-apoptotic gene FLIP in androgen independent prostate cancer PC-3 cells, and that (ii) 2-ME2-mediated tumor growth inhibitory effects were accompanied by transcriptional down-regulation of FLIP through 745 bp (-503/+242) sequence elements. In order to fully understand the underlying molecular mechanism of 2-ME2 induced down-regulation of FLIP, we generated exonuclease deletion constructs and performed transient transfection assays. These studies led to identification of -121/+242 sequence containing putative bindings sites for NFκB, CREB and AR in addition to Sp1 with maximal promoter activity in androgen responsive (LNCaP) and androgen independent (PC-3 and DU145) cells. Using ChIP assays, we also observed the enrichment of these factors to the endogenous FLIP promoter. Furthermore, androgen stimulation enhanced promoter activity and recruitment of Sp1, NFκB to the FLIP promoter region in LNCaP cells. Surprisingly, we found DHT but not R1881 decreased FLIP promoter activity in DU145 cells. Further molecular investigations indicated enhanced expression of AKR1C3 (aldo-keto reductase) that catalyzes the conversion of DHT to 3β-Adiol (a potent ligand for ER-β) in response to 2-ME2 treatment in DU145 cells. In addition, not only 3β-Adiol treatment reduced proliferation of prostate cancer cell significantly but co-transfection with ER-β reduced FLIP promoter activity. Taken together, these results implicate an important role for ER-β/Sp/NFκB/FLIP in mediating 2-ME2 induced tumor growth inhibitory effects. Supported by VA-Merit Award and CA 135451 (APK). Citation Format: Huiyoung Yun, Jianping Xie, Izhar Singh Batth, Rong Li, Rita Ghosh, Addanki Pratap Kumar. ER-β/Sp/NFκB/FLIP axis: Potential therapeutic target in prostate cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4760. doi:10.1158/1538-7445.AM2014-4760