Peroxisome proliferator-activated receptor γ agonist troglitazone induces colon tumors in normal C57BL/6J mice and enhances colonic carcinogenesis in Apc^{1638 N/+} Mlh1^+/- double mutant mice

The role of the nuclear peroxisome proliferator-activated receptor-γ (PPAR-γ) in colon tumorigenesis remains controversial. Notwithstanding evidence that PPAR-γ ligands impede murine colorectal carcinogenesis, PPAR-γ agonists have been shown to enhance in vivo tumor formation in mouse models of human colon cancer. Our study was designed to determine whether troglitazone (TGZ) induces colonic tumor formation in normal C57BL/6J mice and enhances colorectal carcinogenesis in double mutant Apc^1638N/+ Mlh1^+/- mice fed a standard AIN-76A diet. We report herein that not only does TGZ enhance carcinogenesis in the large intestine of mutant mice predisposed to intestinal carcinogenesis but TGZ also induces colonic tumors in normal mice without gene targeting or carcinogen administration. This observation indicates that pre-existing mutational events are not necessary for induction of colonic tumors by activated PPAR-γ in vivo.