AIM: To study whether indomethacin (IND), a nonselective cyclooxygenase (COX) inhibitor or NS-398(NS), a COX-2-selective inhibitor, in duces apoptosis inhuman colon cancer cells and which apoptosis-related genes and pathways are involved.METHODS: Human colon cancer Caco-2 cells were treated with either: placebo, IND (0.05-0.5 mmol/L)or NS (0.01-0.2 mmol/L) for 1, 5 and 18 h. We then studied: (1) Cell death by the TUNEL method, (2) mRNA expression of 96 apoptosis-related genes using DNA microarray, (3) expression of selected apoptosis related proteins by Western blotting.RESULTS: Both IND and NS induced apoptosis in 30%-50% of Caco-2 cells in a dose dependent manner.IND (0.1 mmol/L for 1 h) significantly up-regulated proapoptotic genes in four families: (1) TNF receptor and ligand, (2) Caspase, (3) Bcl-2 and (4) Caspase recruiting domain. NS treatment up-regulated similar pro-apoptotic genes as IND. In addition, IND also down-regulated antiapoptotic genes of the IAP family.CONCLUSION: (1) Both non-selective and COX-2-selective NSAIDs induce apoptosis in colon cancer cell sin a dose dependent manner. (2) Both NSAIDs induce apoptosis by activating two main apoptotic pathways:the death receptor pathway (involving TNF-R) and the mitochondrial pathway. (3) IND induces apoptosis by up-regulating pro-apoptotic genes and down-regulating anti-apoptotic genes, while NS only up-regulates proapoptotic genes. (4) Induction of apoptosis in colon cancer cells by NSAIDs may explain in part, their inhibitory action on colon cancer growth.