Variable cyclooxygenase (COX)-2 expression in Barrett’s associated adenocarcinoma: relationship to tumor differentiation
aCancer Cell Unit, MRC/Hutchison Building, Cambridge, United Kingdom, bThe Adult and Paediatric Gastroenterology Department, Barts and The London School of Medicine and Dentistry, London, United Kingdom, cUniversity College, London
Cyclooxygenase (COX)-2 enzyme catalyses the committed step in the prostaglandin production pathway. Population based studies, animal models and cell line experiments suggest strong association between COX-2 and human cancer. Barrett’s esophageal epithelium (BE) expresses more COX-2 compared with squamous epithelium (NE). However, there is conflicting data regarding COX-2 expression in esophageal adenocarcinoma (AC). Therefore, this study was designed to examine COX-2 expression in BE and associated AC and investigate whether this is affected by the degree of differentiation. Methods COX-2 expression was determined in NE (n=25), BE (n=34), duodenal biopsies, DU (n=15) and AC (n=45), and in Barrett’s cell lines (SEG-1, BIC-1 and OE33) using western blotting and immunohistochemistry. Tumor differentiation was determined using standard histological criteria and villin expression in 30 AC patients. Prostaglandin-E2 (PGE2) levels were measured in organ culture supernatant using enzyme immunoassay (EIA) after 24 hours of incubation. Results COX-2 and PGE2 levels were increased in BE compared with NE (P=0.0003 and P<0.05 respectively). COX-2 expression was, however, variable between AC patients and was heterogeneous within the tumor of the same patient. Grading of differentiation showed 83% agreement between histological criteria and villin immunostaining. Differentiated tumors expressed more COX-2 compared with poorly differentiated tumors, although this did not reach statistical significance. This may be explained by heterogeneity within the tumor, which was demonstrated by immunostaining. This could also explain the low COX-2 levels seen in cancer biopsies using western blotting. The moderately differentiated SEG-1 cell line expressed very high levels of COX-2 whereas the poorly differentiated BIC-1 and OE33 cells did not express significant amounts of the enzyme, in keeping with our immunohistochemistry findings. Conclusion differentiated esophageal AC biopsies and cell lines tend to express more COX-2 than non-differentiated tumors. However, COX-2 expression is heterogeneous within tumors making immunohistochemistry more suitable than western blotting in examining COX-2 expression levels.
Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Nice, France; February 7 - 10, 2004; in poster session 897 (Precursor lesions).