Data from Soluble EP2 neutralizes prostaglandin E<sub>2</sub>–induced cell signaling and inhibits osteolytic tumor growth

Abstract

<div>Abstract<p>Prostaglandin E<sub>2</sub> (PGE<sub>2</sub>) plays a key role in osteolytic bone metastasis as well as roles in inflammation, cell growth, and tumor development. PGE<sub>2</sub> exerts its effects by binding and activating E-prostanoid receptor (EP). In this study, we propose a new approach for blocking EP-mediated cell signaling using a soluble chimeric EP2 fragment. Mammalian expression vectors encoding several human EP2 cDNAs were introduced into 293 cells and the culture medium was tested for their function as a decoy receptor for PGE<sub>2</sub>. PGE<sub>2</sub> binding assays revealed that culture medium containing the second extracellular region of EP2 (FuEP2/Ex2) had binding activity. FuEP2/Ex2 neutralized PGE<sub>2</sub>-induced cyclic AMP production, cyclic AMP–responsive element binding protein phosphorylation, and subsequent induction of cyclooxygenase-2, interleukin (IL)-1β, and IL-6 mRNAs. In human osteoblasts, this culture medium neutralized the induction of receptor activator of nuclear factor-κB ligand mRNA. A stable transfectant expressing FuEP2/Ex2 was established from human prostate cancer PC-3 cells (PC3-FuEP2/Ex2). PC3-FuEP2/Ex2 cells grew at similar rates to vector control cells under normal culture conditions, although PGE<sub>2</sub>-induced growth stimulation was suppressed. Intraosseous injection of PC3-FuEP2/Ex2 cells into the tibia of athymic nude mice revealed that the degrees of tumor growth and osteolysis were decreased compared with control cell-injected mice, with decreased osteoclasts and increased apoptotic cells. Furthermore, the cyclooxygenase-2, IL-1β, and IL-6 mRNA levels were reduced in the tumor lesions. These data suggest that FuEP2/Ex2 is useful for treating osteolytic bone metastasis and cancers that depend on EP signaling for their growth and development. [Mol Cancer Ther 2008;7(9):2807–16]</p></div>