Nonviral gene transfer for cancer gene therapy

Although the pre‐clinical and clinical results of gene therapy have shown promise for some cancers, cancer gene therapy is still at an early stage of clinical development. Due to the complexity of targeted vector delivery to the tumor, our strategy for gene therapy is focussed on the development of local non‐viral gene transfer to treat tumors. The local application of non‐viral gene therapy is of particular value in the context of pre‐ or intraoperative application of therapeutic genes. This ensures accessibility of targeted tumor areas and will contribute to better local control of the disease. In this regard, applicable transfer technologies are needed in gene therapy. Different physical procedures, such as in vivo electroporation, sonoporation, ballistic transfer etc. are employed to deliver naked DNA into the target cells or tissues in vitro and in vivo. Among the various non‐viral gene delivery technologies jet‐injection is gaining increasing acceptance, since this technique allows gene transfer into different tissues with deep penetration of naked DNA. The jet‐injection technology is based on low‐volume jets of high‐velocity to penetrate skin and deeper tissues associated with efficient transfection of the affected area. For non‐viral in vivo gene transfer a jet‐injector prototype was created and tested. The beta‐galactosidase (LacZ), green fluorescence protein reporter gene constructs were successfully jet‐injected into different syngeneic mouse and patient‐derived xenotransplanted human tumor models of colon‐ or mammary carcinoma and malignant melanoma. Qualitative and quantitative expression analysis of jet‐injected tumor tissues revealed the efficient expression of these genes. Therapeutic in vivo experiments using the jet‐injection transfer of the cytosine deaminase suicide gene in tumors demonstrated antitumor effects with significant growth inhibition of the jet‐injected xenotransplanted colon carcinomas. Furthermore, jet‐injection was also successfully used for the application of a heat‐inducible TNF‐α expressing vector system leading to efficient in vivo tumor growth inhibition in the combined non‐viral TNF‐α gene transfer and hyperthermia approach. Based on our pre‐clinical experiments for non‐viral gene transfer, a phase I clinical trial has been conducted at the Clinic for Surgery and Surgical Oncology, Charité, Berlin to evaluate the feasibility, efficiency, and safety of jet‐injection aided LacZ‐reporter gene transfer in patients with cutaneous metastases from breast cancer and malignant melanoma. In this study naked GMP‐plasmid DNA was applied intratumorally by jet‐injection. The jet‐injection was well tolerated by all patients and no side effects have been experienced. The study clearly demonstrated that the single application of plasmid‐DNA is safe and leads to the expression of the LacZ‐reporter gene in the tumor tissue, as shown at mRNA‐ and at protein level.