Radiosensitivity of glioma to Gamma Knife treatment enhanced in vitro and in vivo by RNA interfering Ku70 that is mediated by a recombinant adenovirus

Abstract

The authors sought to evaluate modification of the radiation response of C6 glioma cells in vitro and in vivo by inhibiting the expression of Ku70. To do so they investigated the effect of gene transfer involving a recombinant replication-defective adenovirus containing Ku70 short hairpin RNA (Ad-Ku70shRNA) combined with Gamma Knife treatment (GKT). First, Ad-Ku70shRNA was transfected into C6 glioma cells and the expression of Ku70 was measured using Western blot analysis. In vitro, phenotypical changes in C6 cells, including proliferation, cell cycle modification, invasion ability, and apoptosis were evaluated using the MTT (3'(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide) assay, Western blot analysis, and cell flow cytometry. In vivo, parental C6 cells transfected with Ad-Ku70shRNA were implanted stereotactically into the right caudate nucleus in Sprague-Dawley rats. After GKS, apoptosis was analyzed using the TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling) method. The inhibitory effects on growth and invasion that were induced by expression of proliferating cell nuclear antigen and matrix metalloproteinase-9 were determined using immunohistochemical analyses. The expression of Ku70 was clearly inhibited in C6 cells after transfection with Ad-Ku70shRNA. In vitro following transfection, the C6 cells showed improved responses to GKT, including suppression of proliferation and invasion as well as an increased apoptosis index. In vivo following transfection of Ad-Ku70shRNA, the therapeutic efficacy of GKT in rats with C6 gliomas was greatly enhanced and survival times in these animals were prolonged. Our data support the potential for downregulation of Ku70 expression in enhancing the radiosensitivity of gliomas. The findings of our study indicate that targeted gene therapy-mediated inactivation of Ku70 may represent a promising strategy in improving the radioresponsiveness of gliomas to GKT.