The effect of sulindac, sulfide and sulfone on enzymes mediated by the aryl hydrocarbon receptor pathway in colon cells

1371 Sulindac, a non-steroidal anti-inflammatory drug, as well as its metabolites, sulfide and sulfone have demonstrated chemopreventive capabilities against several forms of cancer, most notably reducing the incidence and mortality of colorectal cancer. The mechanism underlying these effects remains unresolved; however, the metabolites appear to play important roles. In this study, a well-characterized human colorectal adenocarcinoma cell line, Caco-2, was used to investigate the effects of sulindac, sulfide and sulfone on the aryl hydrocarbon receptor (AhR) pathway and enzymes mediated by this pathway. EROD enzyme assays showed significant CYP1A1 activity in cells treated with sulfide (6-fold), and lesser activity in those treated with sulindac (2-fold) and sulfone (1.5- fold). To characterize steady state levels of mRNA, semi-quantitative PCR was conducted. Treatment of Caco-2 cells with 100 μM sulfide increased CYP1A1 mRNA levels by approximately 20-fold over controls, while 100 μM sulindac or sulfone treatment increased levels approximately 2-fold each. To determine whether the effect on steady state levels of CYP1A1 is being regulated through transcription via the AhR pathway, gene regulation experiments are being conducted. The presence of CYP1A1 hnRNA in Caco-2 cells treated with sulindac and sulfide has indicated a transcriptional mechanism for the change in steady state mRNA levels observed. The AhR pathway is the most well-accepted mechanism for CYP1A1 induction and thus its involvement is suggested by these results. As further evidence, luciferase reporter gene assays utilizing the XRE enhancer sequences are being conducted. In addition, electrophoretic mobility gel shift assays are being performed to look for evidence of an activated AhR in the nucleus. Initial results suggest that sulindac, mainly through its sulfide metabolite, interacts with the AhR pathway and induces CYP1A1 activity via XRE-driven transcription. Consequently, this effect may contribute to the protective effect of sulindac against colon cancer.