Combination of anti-cancer drug therapy with targeted gene therapy against glioblastoma.

Abstract

Glioblastoma multiforme (GBM) is the most aggressive and resistant to common therapies primary brain cancer in adults with extremely low percentage of survivors. Therefore, novel therapeutic approaches are greatly needed for these patients. Gene therapy can be a useful adjuvant to conventional therapies such as radiotherapy and chemotherapy. In the past twenty years, numerous gene delivery strategies for cancer, and glioblastoma in particular, have been developed with increasing number of models reaching clinical trials. However, the blood-brain barrier (BBB) is a major obstacle in accessing and treating brain tumours through systemic administration. Work from our laboratory has shown the great potential of a double-targeted Adeno-associated virus/Phage (AAVP) hybrid vector under Glucose-regulated protein 78 promoter (Grp78) (RGD4C/Grp78-AAVP) in targeted systemic cancer gene therapy. Here we investigated the response to combination therapy with suicide gene therapy using Herpes Simplex Virus thymidine kinase (HSVtk) and temozolomide (TMZ). Using a proliferation assay and flow cytometry techniques we demonstrated that RGD4C/Grp78-HSVtk vector mediated stronger cell death in combination with ganciclovir (GCV) and temozolomide than the combination therapy with RGD4C/CMV-HSVtk vector and each therapy alone. Moreover, we showed that temozolomide increases endogenous Grp78 promoter activity and boosts transgene expression mediated by RGD4C/Grp78-AVVP. Also, we demonstrated that RGD4C/Grp78-AAVP vector crosses blood-brain barrier and targets intracranial tumours in mice. Finally, we showed that systemic administration of RGD4C/Grp78-HSVtk and TMZ induces regression of brain tumours in mice. Another approach of targeted therapy for human cancer involves the depletion of key amino acids required for tumours to proliferate e.g. arginine. Recent in vitro studies showed that GBMs lacking argininosuccinate synthetase (ASS) expression are sensitive to arginine depleting enzymes such as arginine deiminase (ADI). In our studies we used a pegylated form of arginine deiminase (ADI-PEG20), to target ASS-negative tumours. We found that ADI-PEG20 can inhibit the growth of ASS-negative glioblastoma tumours in mice. Together, our data demonstrate novel therapeutic strategies against glioblastoma which overcome the limitations imposed by the blood-brain barrier.