Roles of microsomal prostaglandin E synthase-1 in lung metastasis formation in prostate cancer RM9 cells

Cyclooxygenase-2 (COX-2) is known to correlate with a poor prognosis of prostate cancer and contribute to tumor metastasis. However, the precise mechanism of this phenomenon remains unknown. We have previously reported that host stromal microsomal prostaglandin E synthase-1 (mPGES-1) appeared critical for tumor-associated angiogenesis and tumor growth. Here, we tested whether or not mPGES-1 has a critical role in lung metastasis formation of prostate cancer. Murine prostate cancer cells (RM9) were intravenously injected and lung metastasis was estimated by counting colonies in the lungs. Mice treated with a selective COX-2 inhibitor, celocoxib, were suppressed lung metastasis compared to vehicle mice. This lung metastasis formation was also reduced in mPGES-1 knockout (mPGES-1 KO) mice, compared with wild type (WT) mice. This was accompanied with reduced angiogenesis around the metastasized colonies of RM9. Plasma protein levels and metastasized lung tissue mRNA levels of vascular endothelial growth factor (VEGF) and stromal cell derived factor-1 (SDF-1) were significantly suppressed in mPGES-1 KO mice in comparison with WT mice. In addition, the expressions of matrix metalloproteinases (MMP)-9, and metalloproteinases (MMP)-2 were down-regulated in metastatic lungs in mPGES-1 KO mice. These results suggested that host mPGES-1 was essential for MMP-2 and MMP-9 up-regulation that enhances tumor metastasis. mPGES-1 appears to be critical for tumor metastasis in prostate cancers. mPGES-1 inhibitors may be useful to protect against prostate cancer metastasis.