Cytotoxic Effect of Drosophila Deoxynucleoside Kinase Gene on Replicating Plasmid in HeLa Cells

To enhance the levels of transgene expression from plasmid-based nonviral vectors, replicating plasmids containing the SV40 origin and the SV40 large T antigen gene, as a model replicating unit, were constructed. The replicating luciferase plasmid DNA produced the luciferase protein more efficiently than the non-replicating luciferase plasmid DNA, as expected. Surprisingly, the introduction of the replicating plasmid DNA containing the Drosophila melanogaster deoxyribonucleoside kinase (Dm-dNK) gene was highly cytotoxic and caused cell death without nucleoside analogs. Our results confirm that transgenes on a replicating plasmid represent an excellent tool for effective protein production and suggest that efficient production of the Dm-dNK protein in tumor cells could be an attractive cancer therapy.