Expression of COX-2 and 15-PGDH in adenomas removed during pretreatment colonoscopy to predict chemopreventive efficacy of the selective COX-2 inhibitor, celecoxib.

Abstract

524 Background: The APC trial showed that patients at high risk for colorectal adenoma development experienced a 33-45% reduction in post-polypectomy adenoma detection when treated with the selective cyclooxygenase-2 (cox-2) inhibitor, celecoxib. Unfortunately, this study also found a small increased risk of cardiovascular toxicity among celecoxib users, preventing broad use of this agent for chemoprevention. Celecoxib inhibits expression of prostaglandin E2 (PGE2), an inflammatory mediator produced by fatty acid metabolism via cyclooxygenases, and degraded through the activity of 15-prostaglandin dehydrogenase (15-PGDH). Methods: Adenomas collected from APC trial participants prior to treatment were examined using immunohistochemistry (IHC) to assess expression of cox-2 (high vs. low) and 15-PGDH (present vs. absent). A combined variable to estimate tumor PGE2 levels identified cases as PGE2 low (Cox-2 low/15-PGDH present) or PGE2 high (Cox-2 high/15-PGDH present; Cox-2 high/15-PGDH absent; or Cox-2 low/15-PGDH absent). Mantel–Cox test was used to evaluate whether markers of PGE2 expression in these adenomas predicted benefit from celecoxib treatment for the primary study outcome of adenoma detection. Results: Biomarker determinations were achieved for 1295 cases, or 71% of patients with available outcome data. Patients whose baseline adenomas demonstrated elevated Cox-2 achieved the greatest overall reduction in adenoma risk with celecoxib treatment (RR 0.37; p = 0.0001). This risk reduction was less significant in the low Cox-2 category (RR 0.64). Patients with low estimated tumor PGE2 did not benefit from celecoxib for adenoma prevention (RR 0.95; p = 0.83). This is compared to a 41% reduction in adenoma detection with celecoxib treatment for patients in the high PGE2 category (RR 0.59; p < 0.0001). Conclusions: IHC to determine expression of target enzymes in pre-malignant adenomas provides significant prognostic and predictive information in patients treated with celecoxib for prevention of colorectal adenomas.