Abstract 2103: Utilizing ER target genes as biomarkers of endocrine response in serous ovarian carcinoma

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Ovarian cancer is the most common and most lethal gynecologic malignancy. Despite clear histologic and molecular differences between disease subtypes, all patients receive cytotoxic chemotherapy and survival has not improved significantly for several decades. Identifying avenues for targeted therapy is critical to improving clinical outcomes. Given the vast heterogeneity of ovarian cancer, therapeutic strategies will vary based on subtype and specific biomarkers. Estrogen receptor-alpha (ER) is expressed in ∼70% of serous ovarian tumors and epidemiologic evidence indicates estrogen contributes to the disease etiology. Further, clinical data suggest that a subset of patients with serous carcinoma benefit from endocrine therapy. However, the full potential of endocrine therapy in ovarian cancer has been understudied. We hypothesize that a subset of serous ovarian tumors are dependent upon estrogen and that expression of ER target genes will identify patients who can be successfully treated with endocrine therapy. We characterized response to estradiol (E2) in four ER+ serous ovarian cancer cell lines, focusing on cell proliferation, survival, and gene expression. Proliferation was evaluated in 2-D and in a 3-D matrigel system. Survival was assayed in low-attachment conditions. We also evaluated response to anti-estrogens 4-hydroxytamoxifen (4OHT) and fulvestrant (ICI). Expression of canonical ER targets (e.g. GREB1, IGFBP3) was measured by qPCR. Gene expression microarrays after E2 treatment were used to identify genome-wide effects of ER. Studies of endocrine response in vivo are ongoing in patient-derived xenograft models. E2 promotes growth of PEO1 and PEO4 cells in 2-D and 3-D culture, with PEO4 cells exhibiting greater E2 dependence. Preliminary results indicate that E2 also promotes survival in low-attachment conditions. Growth and survival are both decreased by treatment with fulvestrant or 4-hydroxytamoxifen. Conversely, OVCA432 and OVSAHO cells do not respond to treatment with ER ligands. Microarrays identified E2-regulated genes in PEO1 and PEO4 cells that may be utilized as biomarkers of ER activity. Several of these ER targets are differentially expressed between E2-responsive and E2-independent cell lines including DEPTOR, GREB1, GFRA2, and EPHB3. We are currently overlapping our array results with publicly available datasets to develop a gene signature of E2 response, which we will use to profile ER signaling in clinical specimens and patient derived xenografts. Our results suggest that a subset of serous ovarian cancers are endocrine responsive. These studies will determine if expression of specific ER targets correlates with endocrine response and thus if they can be harnessed to predict clinical response to endocrine therapy. Citation Format: Courtney L. Andersen, Matthew J. Sikora, Soumya Luthra, Uma Chandran, Paul Haluska, Steffi Oesterreich. Utilizing ER target genes as biomarkers of endocrine response in serous ovarian carcinoma. [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 2103. doi:10.1158/1538-7445.AM2014-2103