We have previously found that more than 90% of primary GBM tissues and all GBM cell lines examined contain persistently activated Stat3 that promotes the growth of GBM cells in vitro by inducing the bcl-2 family of pro-survival genes including bcl-2, bcl-x and mcl-1. To understand the role of activated Stat3 in the growth of GBM in vivo, we have generated U87MG-derived stable glioma cell lines that express varying levels of a dominant negative mutant (DN)-Stat3 protein in a hypoxia-inducible fashion. Hypoxia and associated cell necrosis and angiogenesis are cardinal features of GBM. A number of representative clones exhibited tight regulation of DN-Stat3 expression under hypoxia in vitro and were selected to determine their tumorigenic potential in nude mice. We found that palpable tumors were formed within two weeks but growth of the tumors from the DN-Stat3 clones were halted once they reached ~2mm in thickness, whereas the parental and vector derived tumors maintained a steady and rapid growth rate. This was likely due to the hypoxia-induced expression of DN-Stat3 as revealed by immunostaining. As evidenced from Kaplan-Meier analysis, the survival time of the mice with orthotopic tumors derived from the DN-Stat3 clones were significantly longer than the control groups. Histological characterization of tissues from the flank tumors by Ki-67 staining showed limited numbers of proliferative cells in the DN-Stat3 clones compared with control group. Analysis of DN-Stat3 expression in relation to HIF-1 expression and areas of hypoxia will also be presented. These data suggest that activated Stat3 may play an essential role in the tumorigenesis of malignant gliomas.
Supported by NIH R01 grants CA095006 to SJH and CA87830 and CA86335 to EGVM.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA