Rat colorectal tumours treated with a range of non-steroidal anti-inflammatory drugs show altered cyclooxygenase-2 and cyclooxygenase-1 splice variant mRNA expression levels

Abstract

Non-steroidal anti-inflammatory drugs (NSAIDs) reduce tumour mass by increasing the rate of tumour cell apoptosis and decreasing cell proliferation. The classically recognized target for NSAID action are the two isoforms of the cyclooxygenase (COX) gene, which is responsible for prostaglandin production. In the rat, the COX-1 gene expresses an alternatively spliced mRNA COX-1 splice variant (SV) which may, at best, code for a truncated COX-1 protein. Previously, we reported that COX-1SV mRNA is differentially expressed in the ageing stomach. In this study, carcinogen treated rats were treated for 23 weeks with celecoxib, sulindac or sulindac sulfone, while untreated rats received vehicle alone. For each animal, the number and volume of tumour per animal was recorded and histology was performed. Using competitive polymerase chain reaction, we determined whether COX gene expression was altered in colorectal tumours and in regions of adjacent and distant macroscopically normal intestine, from vehicle or NSAID treated rats. In addition, we immunolocalized COX-1 and COX-2 in the same tumour and normal colonic tissue. Tumours from animals treated with vehicle or celecoxib expressed significantly elevated levels of COX-2 mRNA in comparison with the adjacent normal mucosa. In contrast, tumours from sulindac and sulindac sulfone treated rats expressed significantly less COX-2 mRNA than tumours from vehicle treated rats. The expression of COX-1 mRNA remained unchanged in all tissues examined. However, COX-1SV mRNA levels were elevated in colorectal tumours and reduced after NSAID treatment to the levels observed in normal colonic mucosa. Our results indicate that the anti-neoplastic actions of NSAIDs may be attributed to COX dependent and/or COX independent mechanisms of action. We also demonstrate the presence and differential expression of COX-1SV mRNA in colon tumours. COX-1SV mRNA represents 2% of the total COX-1 mRNA expressed and its role in colon cancer remains to be established.