Gene Therapy of Malignant Glioma Hanna Stedt Gene Therapy of Malignant Glioma Alternative Strategies and Combination Therapies

Malignant glioma (MG) is the most common malignant brain tumor; its most malignant form, glioblastoma multiforme has a dismal prognosis of ~14 months from diagnosis. Little progress has been made with traditional therapies which consist of a combination of surgery, radiotherapy and chemotherapy. MG is an ideal target for gene therapy due to its spatially restricted localization and rarely metastasizing character. The aims of this thesis were to develop novel gene therapy approaches as well as combination therapies in preclinical in vitro and in vivo MG models. In the first study, Src kinase, a central signaling mediator of oncogenesis, was targeted with lentiviral delivery of small hairpin RNAs (shRNAs). In subcutaneous nude mice xenografts, the inhibition of Src was able to significantly reduce tumor growth and vascularity, whereas in immunocompetent orthotopic rat MG model tumor growth reduction and enhanced survival was only seen with ex vivo transduced tumors. A modest in vivo therapeutic effect was seen in combination with a chemotherapeutic temozolomide (TMZ) and a histone deacetylase inhibitor valproic acid (VPA). In the second study, adenoviral suicide gene therapy of Herpes simplex virus-1 thymidine kinase with the prodrug ganciclovir (HSV-TK/GCV) was combined with TMZ and VPA. In vitro efficient viability reduction, enhanced transduction and bystander effect were demonstrated. In vivo HSV-TK/GCV+TMZ improved the survival and reduced the tumor growth of rats with orthotopic MG but VPA administration conferred no additional benefit. An improved combination therapy schedule was also introduced. In the third study, HSV-TK/GCV therapy was compared with tomato thymidine kinase combined with its specific prodrug, azidothymidine (ToTK/AZT). Both enzymes demonstrated efficacy and substrate specificity in vitro but only mice receiving ToTK/AZT had improved survival compared to non-treated control mice with intracranial MG. No significant differences were observed between the two suicide gene therapies in vivo. In conclusion, Src is a potential target for gene therapy of MG. The efficacy of in vivo therapy was hampered by the low transduction efficiency, which has been recognized as one of the major challenges in gene therapy. Simultaneous administration of GCV with TMZ further enhanced HSV-TK/GCV+TMZ efficacy being of potential value for MG patients. Despite the conflicting findings in the literature, in the current experimental setting, VPA was not able to achieve any further therapeutic benefits warranting for careful optimization of the treatment schedule. ToTK/AZT was found to be an equally efficient alternative for HSV-TK/GCV therapy with favorable therapeutic characteristics. In summary, gene therapy is a potential therapeutic approach for MG although it requires a carefully optimized treatment protocol. National Library of Medicine Classification: QU 470, QU 550, QU 560, QZ 380 Medical Subject Headings: Glioma/therapy; Gene Targeting; Transduction, Genetic; Genetic Vectors; Genes, Suicide; src-Family Kinases/antagonists & inhibitors; RNA, Small Interfering; Lentivirus; Adenoviridae; Thymidine Kinase; Valproic Acid; Ganciclovir; Zidovudine; Disease Models, Animal; Mice; Rats