Role of the prostaglandin receptor EP3 in regulating vasculogenic mimicry of inflammatory breast cancer.

Abstract

Abstract Abstract #2127 Background: Inflammatory breast cancer is an aggressively angiogenic, metastatic and lethal variant of breast cancer. One of the characteristics of aggressive tumors types such as IBC is the ability of tumor cells to undergo vasculogenic mimicry (VM), which is the formation of organized capillary like structures in vitro and in vivo much like endothelial cells, providing a conduit for oxygen and nutrients to reach hypoxic and nutrient deprived tumor cells that have outgrown their adjacent vascular supply. Using genomic and proteomic profiling as well as Western blotting, immunohistochemistry, invasion assays using the modified Boyden chamber assay as well as digital imaging, we evaluated the signal transduction pathways involved in regulating proliferation, invasion, and VM by IBC tumor cells.
 Results: We found that cyclooxygenase-2 (Cox-2), which produces the bioactive lipid, prostaglandin E2 (PGE2) is one gene that is highly expressed IBC tumor cell lines, SUM149 and SUM190. The biological activity of PGE2 occurs via binding of PGE2 to one of 4 members of a G protein coupled receptor family, designated as the EP receptors, EP1, EP2, EP3 and EP4. Western blot analysis and immunochemistry revealed that EP3 receptor protein is produced at very high levels by both IBC tumor cell lines to a significantly (p<0.05) greater extent than either human MCF-7 or MDA-MB-231 non-IBC breast tumor cells. Since EP3 is known to be an inhibitory prostanoid receptor, we evaluated the dose dependent effects of the EP3 agonist, sulprostone, on proliferation, invasion, and VM. Sulprostone [0.1, 1, 10 and 100 μm] inhibited proliferation of SUM149 and SUM190 IBC cells in a dose and time dependent manner to a significantly greater extent (p<0.01) than MCF-7 or MDA-MB-231 breast tumor cells. Sulprostone inhibited invasion of SUM149 IBC tumor cells, with no effect on invasion of a basement membrane by the MDA-MB-231 human non-IBC breast tumor cells. SUM149 IBC tumor cells undergo VM, which was completely inhibited by 10 μM sulprostone at 24 hrs, as visualized by Periodic Acid Schiff (PAS) staining and digital imaging. The ability of sulprostone to completely inhibit VM occurred in conjunction with inhibition of production of laminin 5-γ2 fragments and matrix metalloproteinase-2 (MMP-2) activity. Studies are currently underway to determine the in vivo effect of sulprostone on IBC tumor growth, VM, and metastasis of SUM149 IBC xenografts.
 Discussion: These results suggest that targeting EP3 may provide a selective advantage for abrogating not only proliferation, and invasion but also vasculogenic mimicry that is a key component of the rapid angiogenic program observed in IBC. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2127.