Abstract 4711: Epigenetic modulation restores expression of functional progesterone receptor in endometrial cancer cells

Abstract

Abstract Endometrial cancer, the most common gynecologic malignancy, is a hormonally regulated tumor. Given progesterone is a tumor suppressor in the endometrium, response to progestin-based therapy correlates positively with progesterone receptor (PR) expression. Many endometrial tumors have lost of PR, which limits the clinical application of progestin-based therapy. PRB promoter methylation was reported in 74% of endometrial cancer patients, which correlate with loss of PR expression. These clinical data suggest that restoring PR expression by epigenetic modulation might sensitize tumors to progestin-based therapy. Therefore, we hypothesized that restoring PR expression in endometrial cancer cells will inhibit proliferation and induce cell death. Epigenetic modulators, such as DNA methyltransferase inhibitors (DNMTi) and histone deacetylase inhibitors (HDACi) were evaluated as effective agents to restore PR expression in a panel of endometrial cancer cells. Treatment with the DNMTi 5-aza-2′deoxycytidine (5-aza-dC) or the HDACi LBH589 alone or in combination upregulated PGR mRNA levels. At the protein level, LBH589 treatment upregulated PR by 24 hours and sustained expression for at least 72 hours, even in the presence of progestrone. The upregulated PR expression by LBH589 treatment was dose dependent; an obvious increase in PR was detected with 10 nM LBH589 when compared with control, and the expression reached the highest level at 50 nM to 100 nM. To investigate if the restored PR is functional, we examined PR nuclear localization and expression of target genes. First, after treatment with LBH589 in the absence or presence of progesterone, PR nuclear localization was confirmed by immunostaining and nuclear fractionation followed by Western blotting. Next, a progesterone response element (PRE)-luciferase reporter assay was used to directly examine PR transcriptional activity. LBH589 treatment increased PRE-luciferase activity by 8- to 10-fold in Ishikawa and ECC1 cells. Furthermore, expression of endogeneous PR target genes containing PRE (FoxO1 and cyclin D) or Sp1 element (p21 and p27) was studied in response to LBH589 treatment. Restored PR upregulated FoxO1, p21, p27 and downregulated cyclin D1, demonstrating that PR is functional as a transcription factor. Our findings reveal that epigenetic modulators can restore endogenous PR expression in endometrial cancer cell lines. This preclinical study provides strong support that strategy to re-establish PR expression will result in resensitization of endometrial tumors to progestin therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4711. doi:1538-7445.AM2012-4711