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Cyclooxygenase (COX) is the rate-limiting enzyme that catalyzes the formation of prostaglandins. The inducible isoform (COX-2) has been found to be highly expressed in aggressive metastatic breast cancers, and may play a critical role in tumor progression to metastasis. However, the exact mechanism for COX-2-induced metastasis has yet to be clearly defined. The direct result of COX-2 action is to increase the production of prostaglandins, especially PGE2. We conducted these studies to further correlate the inhibition of COX-2 activity with decreased metastatic potential (i.e., cell proliferation, migration, metalloproteinase expression and focal adhesion complexes). Two estrogen receptor independent, invasive breast cancer cell lines (Hs578T and MDA-MB-231) were used to examine the effects of COX-2 inhibition by two selective COX-2 inhibitors (NS-398 and niflumic acid) on proliferation, migration and metalloproteinase expression by these two cancer cell lines. Proliferation was measured by the standard cell viability staining technique using erythrosin B. The results show a dose-dependent decline in proliferation by both breast cancer cell lines in the presence of either niflumic acid or NS-398 (0.1-100 μM). NS-398 also attenuated cell migration of the MDA-MB-231 cell line in the transwell membrane chambers. Migration was also measured using a scratch wound assay with MDA-MB-231. We report that niflumic acid treatment resulted in impeding the migration and spreading of cells along the wound edge. By 5 hr after scratch wounding a confluent culture, the control cells had closed the wound, where the niflumic acid treated cells had not. We observed a COX-2 inhibitor dose-dependent effect on the metalloproteinases (gelatinases- MMP-2 and -9) mRNA and active protein expression. COX-2 inhibitors may modulate the aggregation of focal adhesion kinase (FAK) and paxillin expression. The studies suggest that COX-2 selective inhibitors will assist in determining and defining the metastatic signaling pathways by which COX-2 may promote the progression of the cancer to a metastatic state. [This research was supported in part by funds from NASA NCC9-112, Georgia Cancer Coalition and NIH grants: RR 03034, GM 08248 and MD 00525].

[Proc Amer Assoc Cancer Res, Volume 46, 2005]