Glioblastoma multiforme (GBM) is the most common and aggressive primary malignant tumor of the central nervous system. GBM has a very low 5-year survival rate and reaching merely a median of ~15 months even with aggressive treatments. PPARγ (Peroxisome proliferator- activated receptor gamma) agonists (ciglitazone), while being widely used on patients of type 2 diabetes mellitus, also have approved anticancer effects. Their action mechanisms on malignant glioma are not fully understood. The aim of this study is to investigate the potential therapeutic effect of PPARγ agonists on maligant glioma. Glioma cell line and in-vivo/ex-vivo animal model intervened by ciglitazone were used to assess the associated mechanism and therapeutic effect. Our results from in vivo and ex vivo experiments showed that ciglitazone not only inhibited tumor growth and its associated angiogenesis, but it also reduced colony formation and migration of tumors. Ciglitazone inhibited the phosphorylation of STAT3 (signal transducer and activator of transcription 3) (at the point of tyrosine 705 by increasing both the amount and activity of SHP-2 (Src homology region 2-containing protein tyrosine phosphatase 2) proteins, based on evidence obtained from immunoprecipitation and immunohistochemistry. Furthermore, ciglitazone activated proteasomes and lysosomes to degrade cell-cycle-related proteins like Cyclin D1, Cyclin E, CDK2 (Cyclin-dependent kinase 2), and CDK4 (Cyclin-dependent kinase 4). Ciglitazone triggered expressions of LC3 (Microtubule-associated protein 1A/1B-light chain 3) and formation of acidic vesicular organelles (AVOs), both of which were implicated in the autophagy pathway. In conclusion, ciglitazone showed the multiple actions to regulate the growth of glioma, which appeared to be a potential candidate for treating malignant glioma.
Keywords: PPARγ; SHP-2; STAT3; glioma; thiazolidinedione.