An Experimental Study On Chemoprevention Of Esophageal Adenocarcinoma By Celecoxib, A Selective Cyclooxygenase-2 Inhibitor

Esophageal adenocarcinoma is found mainly in the lower segment of the esophagus. It is associated with chronic reflux-induced esophageal mucosal injury and the subsequent development of columnar metaplasia in the distal esophagus (Barrett's esophagus). Presently, the incidence of esophageal adenocarcinoma has a worldwide rising trend, especially in western countries in which esophageal adenocarcinoma is the most rapidly increasing cancer. The prognosis for esophageal adenocarcinoma is extremely poor and the 5-year survival rate is only 13%-15%, which has not changed significantly over the last decade. All of these have increased efforts to develop chemopreventive strategies for esophageal adenocarcinoma. Overexpression of cyclooxygenase-2 (COX-2) has been observed in human Barrett's esophagus and esophageal adenocarcinoma. Celecoxib, a new nonsteroidal anti-inflammatory drug, can selectively inhibit COX-2 and has been clinically used in patients with familialadenomatous polyposis to prevent colorectal adenocarcinoma. We think that celecoxib may have a chemopreventive potential for esophageal adenocarcinoma.Objectives: On the basis of a rat model with mixed reflux of acid and duodenal juice, this paper, through several ex vivo and in vivo experimental studies, was aimed to study the feasibility of chemoprevention of esophageal adenocarcinoma by celecoxib, a selective COX-2 inhibitor.Methods: 1. Establishment of a rat surgical model with mixed reflux of acid and duodenal juice and immunohistochemical analysis of COX-2 expression. 80 six-week-old male Sprague-Dawley (SD) rats were randomly divided into two groups: the reflux model group (n=60) and the no-reflux group as a control (n=20). They were allowed to acclimate for 2 weeks prior to surgery. A novel rat surgical model was established by performance of a gastrojejunostomy plus an esophagojejunostomy 5 mm distal to the gastrojejunal anastomosis in rats of the model group. An upper midline laparotomy with blunt manipulation of the abdominal contents was performed in rats of the no-reflux group. 28 weeks after surgery, all animals were sacrificed and the esophageal samples were taken and then opened longitudinally. Pathological changes in the esophagus were examined macroscopically. The esophagus with tumor was carefully examined to determine the maximum dimensions of the tumor, including the width and depth from the mucosa to the outermost border and the craniocaudal span. 8 esophageal samples were randomly and respectively selected from the model and control groups. Two 1-mm-wide longitudinal slices of esophageal tissue including Barrett's and tumor tissue, if present, were removed from each sample. The slices, after snap freezing, were storedat -70 C for further detection of tissue cyclooxygenase-1 (COX-1) and COX-2 protein expression by Western Blotting and tissue prostaglandin E2 (PGE2) level by enzyme-linked imrnunosorbent assay (EL1SA). The remaining esophageal samples were made into paraffin tissue sections. Histopathologic examination and COX-2 expression analysis were performed respectively after hematoxylin-eosin staining and COX-2 immunohistochemical staining. 2. An organ culture experiment of the rat Barrett's esophagus. Esophageal tissue samples with a representative appearance of Barrett's esophagus were selected from the model group. The anastomosis site was identified based on residual surgical sutures. The esophagus was transected 1mm above the anastomosis site. The distal tissue was discarded. The mucosa occupying an irregular area with a reddish appearance in the distal esophagus was carefully stripped off the esophagus and a no more than 1 -mm-wide longitudinal slice of mucosal tissue was removed from it to perform histopathologic examination for identification of Barrett's esophagus. The remaining tissue of Barrett's mucosa was cultured for 24 hours in an organ culture system. Cultured tissue impairment and expression of COX-2 and proliferating cell nuclear antigen (PCNA) were examined respectively in response t...