Abstract Ovarian cancer is the leading cause of death in women with gynecological malignancies and is often called the ‘silent killer’. Thus, new treatment targets are constantly being investigated. PPARγ (Peroxisome Proliferator Activated Receptor gamma) is a nuclear transcription factor that has been implicated in several diseases. However, little is known about PPARγ in ovarian cancer. Recently, PPARγ agonists such as the thiazolinediones (TZDs) have been studied for their potential use as a therapeutic treatment for cancer. In the present study, we investigated the effect of the four TZDs: Rosiglitazone (Rosi), Ciglitazone (CGZ), Troglitazone (TGZ), and Pioglitazone (Pio), on cell proliferation and PPARγ expression in an ovarian cancer cell line: Ovcar3. Treatment with 10 μM CGZ or TGZ for 24 hours decreased proliferation, whereas Rosi and Pio had no effect. We observed that this decrease in Ovcar3 cell proliferation is due to a higher fraction of cells in the G0/G1 stage of the cell cycle. In order to assess whether this was mediated by PPARγ, we investigated the effect of TGZ and CGZ on PPARγ mRNA, protein expression and activity. As Rosi and Pio had no effect on proliferation, only CGZ and TGZ were further investigated. CGZ and TGZ increased PPARγ mRNA expression in Ovcar3 cells (6.9 and 18.1 fold respectively). However, levels of PPARγ protein expression did not correlate with mRNA levels. Moreover, luciferase reporter assays showed that neither of the TZDs increased PPARγ activity. Ovcar3 cells were transfected with a PPARγ overexpression vector (WT) or a mutant dominant negative form of PPARγ (DN). Both CGZ and TGZ increased PPARγ activity when the receptor was over-expressed. Interestingly, the over-expression of WT in unstimulated cells caused an increase in reporter activity, indicating that these cells have the endogenous capacity to mediate PPARγ transactivation. Cells exhibited no changes in proliferation when transfected with the WT or DN forms of PPARγ. Also, the effect on proliferation was not impacted when CGZ or TGZ were added to the WT or DN transfected cells. These findings demonstrate that PPARγ agonists, CGZ and TGZ, stimulate PPARγ expression. However, the decrease in cell proliferation and increased cell cycle arrest seems to be due to both PPARγ dependent and independent mechanisms. These data suggest that the non-PPAR targets of TZDs need to be further investigated. (Supported by NIH RO1 CA 95609-01, and NCRR-P20-RR15592). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1723.