Suppression of pancreatic carcinoma growth by activating peroxisome proliferator-activated receptor γ involves angiogenesis inhibition

AIM: To study the possible actions and mechanisms of peroxisome proliferator-activated receptor gamma (PPAR gamma), a ligand-activated transcription factor, in pancreatic carcinogenesis, especially in angiogenesis. METHODS: Expressions of PPAR gamma and retinoid acid receptor (PXR alpha) were examined by reverse-transcription polymerase chain reaction (RT-PCR) with immunocytochemical staining. Pancreatic carcinoma cells, PANC-1, were treated either with 9-cis-RA, a ligand of RXR alpha, or with 15-deoxy-Delta(12,14) prostaglandin J(2) (15d-PGJ(2)), a ligand of PPAR gamma, or both. Anti proliferative effect was evaluated by cell viability using methyltetrazolium (MTT) assay. A pancreatic carcinoma xenograft tumor model of nude mice was established by inoculating PANC-1 cells subcutaneously. Rosiglitazone, a specific ligand of PPAR gamma, was administered via water drinking in experimental group of nude mice. After 75 d, all mice were sacrificed. Expression of proliferating cell nuclear antigen (PCNA) in tumor tissue was examined with immunohistochemical staining. Expression of vascular enclothelial growth factor (VEGF) mRNA in PANC-1 cells, which were treated with 15d-PGJ(2) or 9-cis-RA at various concentrations or different duration, was detected by semi-quantitative RT-PCR. Effects of Rosiglitazone on changes of microvascular density (MVD) and VEGF expression were investigated in xenograft tumor tissue. Neovasculature was detected with immunohistochemistry staining labeled with anti-IV collagen antibody, and indicated by MVD. RESULTS: RT-PCR and immunocytochemical staining showed that PPAR gamma and RXR alpha were expressed in PANC-1 cells at both transcription level and translation level. MTT assay demonstrated that 15d-PGJ(2), 9-cis-RA and their combination inhibited the growth of PANC-1 cells in a dose-dependent manner. 9-cis-RA had a combined inhibiting action with 15d-PGJ(2) on the growth of pancreatic carcinoma. In vivo studies revealed that Rosiglitazone significantly suppressed the growth of pancreatic carcinoma as compared to control group (0.48 +/- 0.23 cm(3) vs 2.488 +/- 0.59 cm(3), P < 0.05), and the growth inhibition rate was 80.7%. Immunohistochemistry study showed that PCNA was down regulated in Rosiglitazone-treated group compared to the control group. 15d-PGJ(2), 9-cis-RA and their combination inhibited the expression of VEGF mRNA in PANC-1 cells in a dose- and time-dependent manner. MVD was decreased more significantly in Rosiglitazone-treated mice (10.67 +/- 3.07) than in the control group (31.44 +/- 6.06) (P < 0.01). VEGF expression in xenograft tumor tissue was also markedly down-regulated in Rosiglitazone-treated mice. CONCLUSION: Activation of PPAR gamma inhibits the growth of pancreatic carcinoma both in vitro and in vivo. Suppression of tumor angiogenesis by down-regulating the expression of VEGF may be one of the mechanisms by which PPAR gamma activation inhibits the growth of pancreatic carcinoma. (C) 2009 The WJG Press and Baishideng. All rights reserved.