PEA-15 is 15-kDa serine-phosphoprotein that sequesters phospho-ERK from the nucleus to the cytoplasm. Previously, we showed that overexpression of PEA-15 had antitumor effects in both breast and ovarian cancer cells. We also reported that PEA-15 expression was associated with prolonged overall survival in patients with epithelial ovarian cancer, as found using a tissue microarray. Because PEA-15 has two major phosphorylation sites, Serine104 and Serine116, that are closely related to its biological function in regulating cell proliferation and survival, we sought to develop a more potent form of PEA-15 by modifying its two major phosphorylation sites. To determine which mutant form of PEA-15 is a more potent antitumor agent, we evaluated the function of double-mutated PEA-15 at Ser104 and Ser116; PEA-15-AA, in which residues were substituted with alanine (double-unphosphorylated form); and PEA-15-DD, in which residues were substituted with aspartic acid (double-phosphorylated form) were tested in vitro and in vivo in ovarian cancer cell lines. PEA-15-AA resulted in 85% inhibition of SKOV3.ip1 cell colony formation (P<0.001) under anchorage-independent conditions. Compared to vector control, PEA-15-AA reduced projection formation by about 80%-90% (P=0.01) under the 3D Matrigel culture condition and inhibition of cell migration by 60%-80% (P=0.02). Further, to determine the in vivo effect of PEA-15-AA, we injected control vector, PEA-15-AA, and PEA-15-DD stable transfectants of SKOV3.ip1 cells intraperitoneally into nude mice. We observed that PEA-15-AA strongly inhibited tumor formation and tumor size (6 of 15, P=0.02) compared to the control (9 of 10) or PEA-15-DD (16 of 16). Immunohistochemical data revealed that beta-catenin and CD-31 (endothelial cell marker) expression was significantly decreased in PEA-15-AA tumor tissues. These data show that the antitumor effect of PEA-15-AA was partially dependent on both the inhibition of beta-catenin expression and its nuclear translocalization. We next determined the clinical relevance of phosphorylated PEA-15 in patients with ovarian cancer using a human ovarian cancer tissue microarray. Our analysis showed that total double-phosphorylated PEA-15 expression at Ser104 and Ser116 was significantly higher in high-grade (II, P=0.002; III, P=0.001) ovarian tumor tissue than in adjacent normal ovarian tissue. These data indicate that PEA-15 in ovarian tumor cells exists predominantly in the double-phosphorylated form, PEA-15-DD. Further studies are warranted to determine the correlation between the phosphorylation status of PEA-15 and overall survival in patients with ovarian cancer. Taken together, our results suggest that PEA-15-AA has strong antitumor effects in vitro and in vivo that would justify its development as an effective therapeutic molecule in ovarian cancer.

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 5616. doi:1538-7445.AM2012-5616