Improving treatment outcomes in models of glioblastoma cancer

Introduction: Despite the use of treatments, tumour recurrence in glioblastoma (GBM) patients is inevitable, partly because of the blood-brain barrier and the poor perfusion of the tumour vasculature, which act as two major obstacles to effective drug delivery. In order to address the latter, the capacity of liposomal formulations of irinotecan (Irinophore CTM; IrCTM), doxorubicin (Caelyx®) and vincristine to improve vascular function through normalization of GBM vasculature was assessed. In the following studies, the effect of IrCTM on the pharmacokinetics of irinotecan and its therapeutic efficacy in an orthotopic GBM model was compared to administration of the free form of the drug. In addition, siRNA-based therapy was explored as a potential strategy to enhance the efficacy of chemotherapeutics such as irinotecan. In one series of studies, the impact of cationic liposomes used for in vitro ILK (Integrin-Linked Kinase)-targeting siRNA delivery was compared to electroporation. Following successful identification of the most efficacious siRNA delivery method, EGFR and Rictor were selected as therapeutic targets because these proteins are involved in two of the most common molecular pathways reported to be dysregulated in GBM. The therapeutic potential of the combined silencing of EGFR and Rictor was assessed in in vitro and in vivo models of GBM. Results and conclusion: It was found that IrCTM, Caelyx® and liposomal vincristine induce vascular normalization in GBM tumours. It was also demonstrated that IrCTM increases exposure of the brain to irinotecan and its active metabolite SN-38 and improves survival of GBM tumour-bearing animals compared to treatment with free irinotecan. In vitro siRNA transfection using cationic lipids was found to alter the ILK downregulation time course compared to electroporation and to induce changes in pathway signaling that occurred independently of ILK silencing. Combined silencing of EGFR and Rictor reduced cell migration and increased cell sensitivity to chemotherapeutics in vitro. In vivo, dual silencing of EGFR and Rictor led to GBM tumour eradication. In parallel, GBM cell lines expressing red fluorescent proteins were developed as a tool for orthotopic GBM tumour imaging in live animals. These studies demonstrate the potential of siRNA-based therapy targeting EGFR and Rictor to act in combination with optimized chemotherapy agents such as IrCTM to improve treatment outcome in GBM.