Sa1681 Inhibition of the Prostaglandin EP1 Receptor Suppresses Colon Cancer Cell Invasion and Metastasis.

Abstract

Background: The role of cyclooxygenase-2 (COX-2) and its major metabolite prostaglandin E2 (PGE2) in colon carcinogenesis is well established. PGE2 signals through four different receptor subtypes, EP1 - EP4. Elucidation of the role of these receptors in colon tumorigenesis may identify novel targets for therapy, potentially circumventing the side-effects associated with COX inhibition, whilst retaining the anti-cancer properties. We have recently shown that blocking EP1 receptor signalling in a subcutaneous model of colon tumorigenesis reduced tumor growth in vivo. However, whether the EP1 receptor plays a role in colon cancer metastasis is unknown. Aim: To investigate the role of the EP1 receptor in promoting migration, invasion and metastasis of colon cancer cells. Methods: Colon tumor cells (SW480, HT29 and CT26 cells) were treated with an EP1 receptor specific antagonist (ONO-8713), or were stably transfected (CT26 and HT29 cells) with short hairpin RNA (shRNA) targeted against the EP1 receptor (EP1 shRNA) or with scrambled control (Scr shRNA). Changes in cell proliferation, migration and invasion were investigated in vitro. HT29 transfected clones were tagged with a Green Fluorescent Protein (GFP) label for subsequent in vivo studies. 3 x 106 cells were injected into the tail vein of SCID-bg mice and homing of the cells to the brain assessed at day 24 by in vivo confocal microscopy of the mouse skull. After sacrifice, the number of GFP-positive tumors in the liver, kidney and lung was determined. Results: Suppression of the EP1 receptor had no effect on cell proliferation in vitro. In contrast, both migration and invasion of colon tumor cells was significantly reduced by EP1 receptor antagonism and following suppression of EP1 receptor expression. Moreover, suppression of the EP1 receptor in vivo blocked homing of the tumor cells to the brain. Tumor cells were detected in the skull of mice injected with HT29Scr shRNA cells at day 24, but not in the skull of mice inoculated with HT29EP1 shRNA cells. Metastasis of the tumor cells to other organs was also affected by suppression of the EP1 receptor. Conclusion: Suppression of the EP1 receptor reduces colon tumor cell migration and metastasis in vitro and in vivo. Unravelling the mechanisms involving the EP1 receptor in colon cancer metastasis may aid in the search for new therapeutic targets against this malignant disease.