Selective inhibition of cyclooxygenase (COX)-2 inhibits endothelial cell proliferation by induction of cell cycle arrest

High-level expression of cyclooxygenase (COX)-2 is reported in 80-90% of colorectal adenocarcinomas. Selective inhibition of COX-2 was shown to reduce colorectal tumorigenesis in different models of carcinogenesis and to prevent metastasis in xenograft tumor models, as well as to suppress in vitro induced angiogenesis. Recently, COX-2 was reported to be expressed not only in malignant epithelial cells, but also in the neovasculature that feeds the tumor in a variety of solid human cancers. Thus, one of the possible mechanisms by which selective COX-2 inhibitor reduces tumor growth and metastasis is through inhibition of tumor angiogenesis. Although a report suggested a possible role of endothelial COX-1 in the process of angiogenesis, in a recent study, the selective inhibition of COX-2 was shown to strongly inhibit angiogenesis by inducing endothelial cell (EC) apoptosis. In the present study, using human umbilical vein endothelial cells (HUVECs) as a model of angiogenesis, we investigated the potential antiangiogenic effect of the selective COX-2 inhibitor and its mechanism of action, and clearly demonstrated that selective inhibition of COX-2 caused a dose-dependent decrease in the proliferative activity of ECs, as well as an inhibition of capillary-like tube formation. The inhibitory effect on EC proliferation was dependent on the cell cycle arrest to the G1 phase and not on cell apoptosis.