Rosiglitazone inhibits metastasis development of a murine mammary tumor cell line LMM3

Background: Activation of peroxisome proliferator-activated receptors gamma (PPAR gamma) induces diverse effects on cancer cells. The thiazolidinediones (TZDs), such as troglitazone and ciglitazone, are PPAR gamma agonists exhibiting antitumor activities; however, the underlying mechanism remains inconclusive. Rosiglitazone (RGZ), a synthetic ligand of PPAR. used in the treatment of Type 2 diabetes, inhibits growth of some tumor cells and is involved in other processes related to cancer progression. Opposing results have also been reported with different ligands on tumor cells. The purpose of this study was to determine if RGZ and 15d-PGJ(2) induce antitumor effects in vivo and in vitro on the murine mammary tumor cell line LMM3. Methods: The effect on LMM3 cell viability and nitric oxide (NO) production of different doses of RGZ, 15-dPGJ(2), BADGE and GW9662 were determined using the MTS colorimetric assay and the Griess reaction respectively. In vivo effect of orally administration of RGZ on tumor progression was evaluated either on s.c. primary tumors as well as on experimental metastasis. Cell adhesion, migration (wound assay) and invasion in Transwells were performed. Metalloproteinase activity (MMP) was determined by zymography in conditioned media from RGZ treated tumor cells. PPAR gamma expression was detected by immunohistochemistry in formalin fixed tumors and by western blot in tumor cell lysates. Results: RGZ orally administered to tumor-bearing mice decreased the number of experimental lung metastases without affecting primary s.c. tumor growth. Tumor cell adhesion and migration, as well as metalloproteinase MMP-9 activity, decreased in the presence of 1 mu M RGZ (non-cytotoxic dose). RGZ induced PPAR gamma protein expression in LMM3 tumors. Although metabolic activity -measured by MTS assay- diminished with 1-100 mu M RGZ, 1 mu M-treated cells recovered their proliferating capacity while 100 mu M treated cells died. The PPAR gamma antagonist Biphenol A diglicydyl ether (BADGE) did not affect RGZ activity. On the contrary, the specific antagonist GW9662 completely abrogated RGZ-induced decrease in cell viability. A decrease in NO levels was detected in the presence of either 1 or 100 mu M RGZ. The natural ligand 15d-PGJ2 did not affect metabolic activity although it induced a significant decrease in NO production. Conclusion: A significant decrease in the number of experimental LMM3 lung metastasis, but not on primary tumor growth, after oral RGZ administration was observed. In vitro, 100 mu M RGZ also reduced cell viability and NO production, while no changes were observed in the presence of 15d-PGJ(2). BADGE did not reverse RGZ effect while the antagonist GW9662 completely abrogated it, suggesting a PPAR gamma-dependent mechanism. Inhibition of lung metastatic nodules by RGZ administered in vivo, might be associated with the observed decrease in MMP-9 expression, in cell adhesion, migration and invasion. RGZ augmented its expression. PPAR gamma was detected in cell lysates by western blot and by immunohistochemistry in tumors from RGZ-treated mice. In summary we can suggest that RGZ or any other TZDs might be possible future approaches in the treatment of metastasis of PPAR gamma-expressing cells.