Nonsteroidal anti-inflammatory drugs (NSAIDs) have been demonstrated to suppress colorectal tumorigenesis. NSAIDs have also been used to treat inflammatory illnesses. However, the underlying mechanisms of action by NSAIDs have not been completely elucidated. In this study, we reported that among the six members of the multidrug resistance protein gene (MRP1 to MRP6) family which encode membrane transporters for a diverse group of antitumor agents, expression of MRP1 and MRP3 but not the others in human colorectal cancer cell lines was induced by sulindac. This induction profile is consistent with the results using prooxidants which produce reactive oxygen species (ROS) and generate oxidative stress as previously reported. Moreover, treatment of colorectal. cancer cells with sulindac induced ROS. Suppression of ROS formation by antioxidant N-acetylcysteine (NAC) downregulated the induction of MRP1 and MRP3 expression. Expression of another oxidative stress-sensitive gene, gamma-glutamyleysteine synthetase heavy subunit gene (gamma-GCSh), which encodes the rate-limiting enzyme in glutathione biosynthesis, was also induced by sulindac. However, the suppression of sulindac-induced gamma-GCSh expression by NAC was less sensitive compared with that of MRP1 and MRP3. We also demonstrated that induction of MRP3 and gamma-GCSh was independent of intracellular COX-2 levels. These results, collectively, suggest a ROS-related, COX-2-independent mechanism for the induction of drug resistance gene expression that bears important implications to the roles of NSAIDs in colorectal carcinogenesis and inflammatory response. (C) 2002 Elsevier Science (USA).