672. Hybrid AAV/Phage Vector Enhances Chemotherapy Efficacy Against Cancer

Abstract

Chemotherapy has been widely used for cancer treatment, both in early and late stages. However, chemotherapy does not selectively target tumor cells, as normal cells are also harmed by the drugs resulting in several side effects. Another major obstacle to the success of chemotherapy in cancer treatment is the development of tumor drug resistance by cancer cells. In order to avoid these problems, the combination of chemotherapy with other therapeutic strategies has been used in order to lower the chemotherapeutic drug dose. Gene therapy is one of the therapeutic strategies that can be combined with chemotherapy. Mammalian viruses are well recognized vehicles for gene therapy, but major drawbacks of these viral vectors are broad tissue tropism following systemic administration (low specificity for the target cells/tissues), their fragility to harsh environments and difficulty for large scale production. Therefore, our group has developed a vector from bacteriophage, a bacteria virus also named phage. This novel engineered phage, called AAV/Phage, displays the RGD4C peptide to target a specific receptor (αvβ3 integrin) on cancer cell surface, while the phage genome is merged with recombinant rAAV2 virus genome carrying the transgene to deliver. In comparison with mammalian viral vectors, the production of AAV/Phage is quicker, simpler and more economical. In addition, the vector is stable at 4oC for many years. The AAV/Phage vector efficiently targeted, delivered, and expressed transgene in cancer cells in vitro. We also proved that the vector selectively targeted gene delivery to tumors after intravenous injection in animal models of cancer. Moreover, in brain tumor models, the vector can penetrate through blood brain barrier and selectively delivers transgene expression to brain tumors. We used our vector as combination therapies with some well-known cancer drugs, such as doxorubicin, and temozolomide. Combination treatment of AAV/Phage vector carrying the Herpes Simplex virus thymidine kinase gene (AAV/Phage-HSVtk.) with doxorubicin increased the targeted cancer cell killing in 2D tissue cultures and 3D tumor spheroids of rat gliosarcoma (9L) and human melanoma (M21) cells. We found that this increase in tumor cell killing was associated with a synergistic effect of doxorubicin on enhancing gene expression by AAV/Phage. We then combined AAV/Phage carrying short hairpin RNA to suppress mTOR gene expression (AAV/Phage-shmTOR) with temozolomide to treat medulloblastoma cells (DAOY). The results exhibited that treatment of medulloblastma with the vector alone efficiently suppresses the expression of mTOR gene, but has no effect on cell killing. Treatment of temozolomide at low dose (500 uM) did not have effect on cell killing, but combination therapies of temozolomide with AAV/Phage-shmTOR significantly increased cell death. Altogether, our results demonstrate that combination of AAV/Phage carrying therapeutic genes with cancer chemotherapeutic drugs is an effective strategy for cancer treatment. In future work, we plan to investigate the efficacy of AAV/Phage and cancer drug combination treatment in pre-clinical models of cancer.