In this study, we investigated the inhibitory effect of
clofibric acid (CA), a
ligand for
peroxisome proliferator-activated receptor (
PPAR)alpha, and
pioglitazone, a
ligand for
PPARgamma, on
ovarian cancer in in vivo experiments using human
ovarian cancer cell lines, and we aimed to elucidate the molecular mechanism of their anticancer effect. The antitumor effects of CA (3,000 ppm in the daily diet),
pioglitazone (240 ppm in the daily diet) or the combination were studied in female nu/nu mice, xenografted with subcutaneous OVCAR-3
tumors or with intraperitoneal DISS
tumors. The
tumor tissues were quantified for expression levels of
AP-1,
cyclooxygenase-2 (COX-2) and
vascular endothelial growth factor (
VEGF) using Western blot analysis or immunohistochemistry. CD-31-stained microvessel density (MVD) was measured in the
tumors. The induction of apoptosis was quantified by the TUNEL method. Treatment with CA or
pioglitazone significantly suppressed the growth of subcutaneously xenotransplanted OVCAR-3
tumors and prolonged the survival of mice with malignant
ascites derived from DISS cells as compared to the control. Combination of both agents enhanced the anticancer effect. Increase of apoptosis and
necrosis as well as decrease of
VEGF expression and MVD were found in solid OVCAR-3
tumors treated with CA,
pioglitazone or the combination. The combination significantly induced apoptotic cells, compared to CA or
pioglitazone alone. The combination significantly reduced expression of
AP-1, which is a transcriptional regulator of COX-2, and also significantly decreased COX-2 expression in OVCAR-3
tumors compared to the control, CA or
pioglitazone alone, although CA or
pioglitazone alone decreased them with a marginal significance compared to the control. These findings indicate that the combination of CA and
pioglitazone produces a potent antitumor effect on
ovarian cancer through reduction of
AP-1 expression.