Development and characterization of an enhanced nonviral expression vector for electroporation cancer treatment

Nonviral plasmid DNA gene therapy represents a promising approach for the treatment of many diseases including cancer. Intracellular delivery of DNA can be achieved with the application of electroporation, which facilitates the initial transport of exogenous DNA across the cell membrane into the cytoplasm. However, it does not guarantee further transport of the DNA from the cytoplasm to the nucleus for subsequent mRNA expression, resulting in varying degrees of exogenous gene translation and a major limitation in comparison to viral approaches. To overcome these expression difficulties, we developed a proof-of-concept vector enhanced expression vector (EEV), which incorporates elements from viral systems including nuclear localization sequences and a viral replicase from the Semliki Forest virus. The replicase allows for cytoplasmic mRNA expression and bypasses the need for nuclear localization to generate high levels of gene expression. We have demonstrated that our EEV is capable of achieving high levels of expression in a variety of tissue types. Antitumor effects of pEEV were demonstrated by the delayed growth and increased survival of the nontherapeutic pEEV-treated CT26 tumor model. Using a novel endoscopic electroporation system, EndoVe, we demonstrate and compare, for the first time, both standard cytomegalovirus (CMV) promoter-driven plasmid and EEV gene expression in intraluminal porcine tissues. Our EEV plasmid displays reliable and superior expression capability, and due to its inherent induced oncolytic activity in transfected cells, it may enhance the efficacy and safety of several cancer immunogene therapy approaches.