Efficacy of systemic temozolomide‐activated phage‐targeted gene therapy in human glioblastoma

Glioblastoma multiforme (GBM) is the most lethal primary intracranial malignant neoplasm in adults and most resistant to treatment. Integration of gene therapy and chemotherapy, chemovirotherapy, has the potential to improve treatment. We have introduced an intravenous bacteriophage (phage) vector for dual targeting of therapeutic genes to glioblastoma. It is a hybrid AAV/phage, AAVP, designed to deliver a recombinant adeno‐associated virus genome (rAAV) by the capsid of M13 phage. In this vector, dual tumor targeting is first achieved by phage capsid display of the RGD4C ligand that binds the α v β 3 integrin receptor. Second, genes are expressed from a tumor‐activated and temozolomide (TMZ)‐induced promoter of the glucose‐regulated protein, Grp78 . Here, we investigated systemic combination therapy using TMZ and targeted suicide gene therapy by the RGD4C/AAVP‐ Grp78 . Firstly, in vitro we showed that TMZ increases endogenous Grp78 gene expression and boosts transgene expression from the RGD4C/AAVP‐ Grp78 in human GBM cells. Next, RGD4C/AAVP‐ Grp78 targets intracranial tumors in mice following intravenous administration. Finally, combination of TMZ and RGD4C/AAVP‐ Grp78 targeted gene therapy exerts a synergistic effect to suppress growth of orthotopic glioblastoma. Synopsis Following intravenous administration, the RGD4C/AAVP‐Grp78 vector delivers the therapeutic AAV genome into GBM via binding to integrins. Treatment with temozolomide (TMZ) induces the Grp78 promoter activity and subsequently the therapeutic gene expression resulting in synergistic anti‐tumor action. RGD4C/AAVP‐Grp78‐HSVtk binds to α v β 3 integrin in GBM, leading to vector internalisation and delivery of the recombinant rAAV genome in the nucleus to generate expression of the HSVtk. Expression of HSVtk results in phosphorylation of ganciclovir (GCV) within GBM and subsequent tumor destruction. Administration of TMZ induces the Grp78 promoter activity through the UPR pathway, resulting in further expression of the HSVtk and subsequent phosphorylation of GCV. Consequently combination of TMZ with targeted intravenous RGD4C/AAVP‐Grp78‐HSVtk/GCV gene therapy results in synergistic destruction of GBM. Graphical Abstract Following intravenous administration, the RGD4C/AAVP‐Grp78 vector delivers the therapeutic AAV genome into GBM via binding to integrins. Treatment with temozolomide (TMZ) induces the Grp78 promoter activity and subsequently the therapeutic gene expression resulting in synergis