286. Systemic Delivery of AAV9-IFNβ Vectors for Glioblastoma Gene Therapy

Introduction: Glioblastoma multiforme (GBM) is the most prevalent primary brain tumor, with a median survival (MS) of only 14.6 months from diagnosis despite providing multimodal treatment including maximal surgical resection, radiation and chemotherapy. Due to the highly invasive properties of GBM cells, complete surgical resection is practically impossible, leading to tumor recurrence and death. Thus, new approaches are needed to prevent tumor recurrence.IFNb is a pleiotropic cytokine with potent anti-tumor effects. Previous studies have shown that local delivery of AAV-IFNb in a non-invasive GBM mouse model had a remarkable therapeutic effect. However local treatment may be insufficient to treat GBM where long distance migration is a common feature. Therefore the therapeutic approach should be matched to the tumor properties, which may be accomplished with a disperse therapeutic network generated by global brain gene delivery. Here we tested the therapeutic efficacy of an AAV9-IFNb vector infused via the tail vein in an orthotopic xenograft GBM model in athymic nude mice implanted in the striatum with 50,000 highly invasive GBM8 human glioblastoma cells stably expressing firefly luciferase (GBM8-fluc) for in vivo bioluminescence monitoring of tumor growth. AAV9-IFNb vector was infused via the tail vein at different times after tumor implantation.We performed a dose response study by infusing AAV9-IFNb vectors at different doses (1E11vg to 1E12vg/mouse) on d14 posttumor implantation. The improvement in survival with AAV9-IFNb was dose dependent and ranged from an increase in median survival of 111 days to complete tumor regression compared to 46 days in PBS-treated controls. Treatment with 3e11vg AAV9-IFNb resulted in the survival of 87.5% of animals for at least 8 months with no remaining evidence of GBM cells in the brain upon histological examination. This dose was considered the minimal effective dose (MED) and used in subsequent experiments. Next, we examined the impact of time between tumor implantation and treatment by infusion AAV9-IFNb at MED on d14, d21, d25 or d28. We found that d21 is the longest interval showing 100% long-term survival. Interestingly, the survival benefit was drastically reduced when treated on d25 or later, corroborated by Fluc imaging results and histological analysis showing untreated GBM growth accelerates considerably after d21.Finally, we tested the importance of global gene delivery in a model of multifocal GBM model with tumors implanted in both hemispheres. On d14, AAV9-IFNb was infused systemically at MED or injected intratumorally on one side of the brain. We found that systemic delivery resulted in reduction of tumor size in both hemispheres while intra-tumoral injection only impacted tumor growth on the injected side. All animals treated systemically with AAV9-IFNb survived long-term, while the median survival for animals receiving a unilateral injection of AAV9-IFNb was 57 days compared to 46 days for PBS-treated controls.Conclusion: Global delivery of AAV9-IFNb can be beneficial particularly to treat invasive or multifocal GBM and can provide long-term survival in the xenograft GBM model when treated before the onset of highly accelerated tumor growth.