THE EFFECT OF SULINDAC AND ITS METABOLITES ON ENZYMES MEDIATED BY THE ARYL HYDROCARBON RECEPTOR PATHWAY IN COLON CELLS

Abstract

Sulindac, a non-steroidal anti-inflammatory drug, as well as its metabolites, sulindac sulfide (sulfide) and sulindac sulfone (sulfone) have demonstrated chemopreventive capabilities against several types of cancer, most notably reducing the incidence and mortality of colorectal cancer. The biochemical mechanism underlying these effects remains unresolved, however. Sulindac has been shown to inhibit pol.ycyclic aromatic hydrocarbon-induced tumorigenesis in various rodent models. Polycyclic aromatic hydrocarbons are detoxified by a series of enzymes that are primarily under the control of the aryl hydrocarbon receptor (AhR). We therefore hypothesized that modulation of the activity and expression of these enzymes by sulindac or its metabolites may be responsible for the reported chemoprotective effects. In the present study, a wellcharacterized human colorectal adenocarcinoma cell line, LS 180, was used to investigate the effects of sulindac, sulfide and sulfone on the AhR pathway and enzymes mediated by this pathway. Sulfide treatment resulted in a sustained, dose-dependent increase in cytochrome p450 (CYP) enzyme activity in colon cells. Sulindac caused a more modest, yet sustained increase in CYP activity, while sulfone induced only minor increases at high concentrations. To characterize steady state levels of mRNA, semi-quantitative PCR was conducted. Sulindac and sulfide induced substantial, dose-dependent increases in the mRNA of all three CYP enzymes. Sulfide treatment caused greater increases in CYP mRNA compared to sulindac, while sulfone caused much less of an increase. Thus, the RT-PCR data is in agreement with the enzyme activity data. None of the compounds induced quinone reductase enzyme activity or mRNA levels. Sulindac and sulfide induced CYP activity via a transcriptional mechanism as indicated by the elevated level of heterogeneous nuclear CYP1A1 and CYP1131 RNA present in treated cells. Whether or not this activity was due to direct interaction with the AhR however, remains unclear. Sulfide, but not sulindac was able to activate the XREbinding capacity of the AhR as indicated by gel shift assays. Neither sulindac nor sulfide was able to displace TCDD from the AhR. in ligand binding experiments however. The mechanism by which sulindac and sulfide induce CYP activity and expression therefore, remains unknown. Together, these results indicate that sulindac, most notably through its sulfide metabolite, induces phase I CYP enzyme activity and expression in colon cells. Because CYP induction is the first step in the detoxification of many environmental carcinogens, this activity may contribute to the protective effect of sulindac against colon cancer.