Dose-dependent modulation of apoptosis and cyclooxygenase-2 expression in human 1547 osteosarcoma cells by NS-398, a selective cyclooxygenase-2 inhibitor. A selective cyclooxygenase-2 (COX-2) inhibitor, NS-398, was shown to produce an anti-proliferative and pro-apoptotic effect on different types of cell lines. We describe the presence of COX-1 and COX-2 pathways in the human osteosarcoma 1547 cell line, as well as the conflicting effects of NS-398 (10, 50 and 100 microM) on programmed cell death, PGE2 release and COX-2 expression in 1547 cells cultured under apoptotic conditions. We demonstrate a link between the effects of 10 and 100 microM NS-398 on cell apoptosis, PGE2 release, and expression of COX-2 in 1547 cells undergoing apoptosis. At 10 microM, NS-398 acted as a selective COX-2 inhibitor moderately increasing apoptosis without any effect on COX-2 expression. In contrast, at 100 microM, NS-398 induced a cell cycle slowing or arrest, strongly enhanced COX-2 expression which was associated with a high PGE2 release and a marked decrease in apoptosis. This latter property of NS-398 at 100 microM in 1547 human osteosarcoma cells is novel compared to the described NS-398 pro-apoptotic effect on other cell lines.