Troglitazone inhibits tumor growth in hepatocellular carcinoma in vitro and in vivo

Peroxisome proliferator-activated receptor gamma (PPAR gamma) has been implicated in the differentiation and growth inhibition of cancer cells. We examined the effects of PPAR gamma activation by troglitazone on hepatocellular carcinoma (HCC) cell growth, proliferation, and apoptosis in vitro and in vivo. We also studied relationships between PPAR gamma activation and cyclooxygenase-2 (COX-2) expression. Human HCC cell lines Huh7 and Hep3B were cultured in the presence or absence of troglitazone. Cell growth was determined via WST-1 assay, proliferation by cell cycle analysis and proliferating cell nuclear antigen (PCNA) Western blotting, and apoptosis by flow cytometry and TUNEL. Tumor growth after subcutaneous implantation of Huh7 cells in nude mice was monitored, and the effects of treatment with troglitazone were determined. In resected HCCs, PPAR gamma expression was less compared with the histologically normal surrounding liver. In cultures of Hep3B and Huh7 cells, basal expression of PPAR gamma was relatively low, but troglitazone caused dose-dependent induction of PPAR gamma expression. Cell cycle analysis revealed a decreased proportion of cells in S phase, with arrest at G0/G1. Concomitant downregulation of PCNA and an increase in TUNEL staining, cells were consistent with decreased proliferation and induction of apoptosis by troglitazaone. Troglitazone-mediated PPAR gamma activation also suppressed COX-2 expression and induced p27 in HCC cells. Administration of troglitazone to Huh7 tumor-bearing mice significantly reduced tumor growth and caused tumor regression. In conclusion, collectively, these results indicate that PPAR gamma could be a regulator of cell survival and growth in HCC. PPAR gamma therefore represents a putative molecular target for chemopreventive therapy or inhibition of liver cancer growth. Supplementary material for this article can be found on the HEPATOLOGY website (http://interscience.wiley.com/jpages/0270-9139/suppmat/index.html).