The inhibitory effect of PEDF in glioma tumors

3017 Malignant gliomas are highly vascularized and invasive neoplasms, which are characterized by a high incidence of recurrence and a poor prognosis. The progressive growth of glioblastoma is thought to be dependent on angiogenesis. Recent studies have shown that pigment epithelium-derived factor (PEDF) can induce differentiation and inhibit angiogenesis of several tumors. In this study, we investigated the effect of PEDF on glioma cell (U87 and A172) growth and angiogenesis by TUNEL and Flow cytometry. Results indicated that the rPEDF-treated cells had a significantly higher percentage of apoptotic cells when compared with the control cells. More analysis of the cell cycle showed that the rPEDF treated cells would arrest in the G(1) phase and block in S phase of the cell cycle. We found that the apoptosis of glioma cells caused by rPEDF is associated with a marked increase of p53 and Bax as well as the down-regulation of Bcl-2. Glioma cells treated with rPEDF exhibited decreased invasiveness. The anti-migratory activity of rPEDF was evident even in the presence of the vascular endothelial growth factor (VEGF), an inducer of glioma indicating that its effect on glioma cells migration was powerful. Real-time PT-PCR and Western-blot were used to evaluate whether rPEDF would affect the production of positive and negative factors of angiogenesis. Glioma cells exhibited a decreased expression of VEGF and an increased expression of TSP-2 (the major negative angiogenic factors in glioma). Both changes were essential and sufficient to shift the angiogenic phenotype of glioma cells to anti-angiogenic. The angiogenic switch seen in vitro was maintained in vivo , where PEDF-expressing cells formed small glioma nodules with reduced vascularization. The rPEDF treatment regimen resulted in significant reduction in the tumor size in 2 weeks compared with the control group after the formation of the glioma tumors. The mechanism underlying the suppressed growth appears to be the anti-angiogenesis function of PEDF. A 55 % decreased MVD in the PEDF-treated glioma closely paralleled the 53 % decreased tumor size inferring a direct relationship between glioma vascularity and growth. Our results demonstrated for the first time that PEDF could significantly reduce the gliomas angiogenesis, proliferation, and migration in vitro and in vivo . Our study presents a novel approach of developing anti-angiogenic therapies to treat gliomas.