Abstract 1619: ERK-targeted therapy suppresses tumorigenicity in ovarian clear cell carcinoma and is modulated by ERK-binding protein PEA-15

Ovarian clear cell carcinoma (CCC) has shown resistance to the current standard chemotherapy used for epithelial ovarian cancer (EOC). Therefore, developing a novel therapeutic strategy is imperative to improve the prognosis for patients with CCC. Epidermal growth factor receptor (EGFR) is frequently expressed in EOC. PEA-15 is a 15-kDa phosphoprotein that slows cell proliferation by binding to and sequestering ERK in the cytoplasm. The purpose of the current study was to determine whether the EGFR-ERK pathway is a therapeutic target in CCC and whether PEA-15 modulates ERK-targeted therapy in CCC. We screened a panel of four CCC cell lines (RMG-I, SMOV-2, OVTOKO and KOC-7c) and performed Western blotting to detect the expression levels of EGFR, pEGFR, ERK and pERK. RMG-I and SMOV-2 showed high EGFR expression, while OVTOKO and KOC-7c showed lower expression. We next performed WST-1 assay and showed that erlotinib inhibited cell proliferation in high EGFR-expressing cell lines (IC 50 = 0.1 μM for RMG-I and 1 μM for SMOV-2) by suppressing pEGFR and pERK expression and inducing G 1 arrest. Further, transfection with constitutive active MEK1 significantly reduced the sensitivity to erlotinib in RMG-I cells (p Therefore, we hypothesized that ERK inhibition suppresses tumorigenicity in CCC. We examined the sensitivity of CCC to MEK inhibitor AZD6244 (ARRY-142886) and observed that the erlotinib-sensitive cell lines were also sensitive to AZD6244 (IC 50 = 0.79 μM for RMG-I and 0.85 μM for SMOV-2) by suppressing pERK expression and inducing G 1 arrest. We next investigated the possible mechanistic role of PEA-15 in the therapeutic effect of the ERK-targeted therapy with AZD6244. Phosphorylated PEA-15 at ser116 [pPEA-15(S116)] levels increased after AZD6244 treatment in the sensitive cell lines. Transient transfection with phosphomimetic mutant PEA-15 (S116D) reduced cell viability, sensitizing the insensitive cell lines to AZD6244, implying that pPEA-15 (S116) confers sensitivity to AZD6244 in CCC cells. Further, both AZD6244 (50mg/kg/d) and erlotinib (100mg/kg/d) significantly suppressed tumor growth (p We concluded that the MEK/ERK pathway is a potential therapeutic target for CCC and that AZD6244 is worth exploring as a therapeutic agent for patients with CCC. Further studies are warranted to determine if PEA-15 may be useful to predict sensitivity to ERK-targeted therapy in CCC. 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 1619.