Abstract 4789: Functional characterization and clinical correlation of the tumor antigen casein kinase 1-epsilon in ovarian cancer

Abstract

Abstract OBJECTIVES: Prior studies have identified antibodies to casein kinase I epsilon (CKI-ε) in the serum of patients with ovarian cancer. We investigated the expression pattern, functional roles, and clinical correlation of CKI-ε in ovarian cancer. METHODS: The expression of CKI-ε in 8 healthy ovaries and 68 ovarian tumor samples was determined by IHC and scored on intensity of antibody expression (scale 0-3) and the percentage of the area stained (scale 0-3). The average from both scores was assigned to each patient. Clinical characteristics for each patient were retrieved from electronic medical records. Statistical significance was determined using the Fisher exact test. Univariate analysis was performed by constructing probability curves according to the Kaplan-Meier method. Immortalized normal human ovarian surface epithelial (HOSE) cell lines with ectopic expression of CKI-ε were established by transfection with a CKI-ε expression construct. CKI-ε-targeting shRNAs were used to generate ovarian cancer cell lines that have stably suppressed CKI-ε expression. Protein expression was determined by Western blot. Growth rate was determined by cell counting. Three-dimensional spheroid culture was performed on Matrigel. The growth of ovarian cancer cell lines harboring either a control shRNA or a CKI-ε-shRNA was evaluated in a mouse xenograft model. The effects of IC261, an inhibitor of CKI-ε, on ovarian cancer cells were evaluated by MTT assay. RESULTS: CKI-ε was overexpressed in 67% of invasive ovarian tumors (P-value=0.001) and in 14 of 17 ovarian cancer cell lines. Normal HOSE cells that have ectopic expression of CKI-ε have accelerated growth rate and formed spheroids in Matrigel that were two to four times larger than those formed by control HOSE. In contrast, cancer cell lines harboring specific CKI-ε shRNA had reduced growth rate and 6-fold reduced tumor weight in the xenograft model (P-value=0.007). The cancer cell lines also showed CKI-ε-dependent sensitivity to IC261. The median CKI-ε expression level among the ovarian cancer tissue samples was 3. For patients whose score was ≤ 3 and > 3, the mean overall survival was 91 months and 48 months, respectively. Similarly, the mean disease free survival interval was 43 months and 22 months for patients whose score was ≤ 3 and > 3, respectively. Patients who scored > 3 tended to have late stage disease (61%) compared to patients who scored ≤ 3 (39%), (p=0.06). CONCLUSIONS: CKI-ε is highly expressed in ovarian tumors and cancer cell lines. Studies of cell lines with alterations in CKI-ε expression showed that this signaling protein regulates cell growth and survival. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4789.