Targeted over-expression of mPGES-1 and elevated PGE₂ production is not sufficient for lung tumorigenesis in mice

There is a significant body of evidence suggesting that enzymes involved in arachidonic acid metabolism and their eicosanoid products play a role in various cancers, having both pro- and antitumorigenic effects. The goal of this study was to further define the role microsomal prostaglandin E synthases (mPGES-1) play in lung tumorigenesis. Transgenic mice were created with targeted over-expression of human mPGES-1 in the alveolar and airway epithelial cells using an SP-C promoter driven construct. Transgene positive (mPGES-1⁺) mice were shown to significantly over-express functional mPGES-1 in the lung and more specifically in alveolar type II cells. To study the effects of mPGES-1 over-expression in lung tumor formation, mice were exposed to a complete carcinogen protocol with a single injection of urethane or an initiation/promotion model with a single injection of 3-methyl-cholanthrene (MCA) followed by multiple injections of butylated hydroxytoluene (BHT). mPGES-1⁺ mice did not show a significant difference in tumor multiplicity or tumor size at 10, 16, 19 or 30 weeks after urethane injection compared with mPGES-1^- mice. No significant difference was seen in tumor incidence, multiplicity or size at 19 weeks after treatment with MCA/BHT. Western blots verified that mPGES-1 expression was increased in tumors versus uninvolved tissue of both mPGES-1⁺ and mPGES-1^- mice with overall expression being significantly higher in mPGES-1⁺ mice. Cyclooxygenase-2 levels were elevated in tumors in both groups. From these studies we conclude that over-expression of mPGES-1 and highly elevated PGE₂ production are not sufficient to induce lung tumors.