Background: Electroporation of skeletal muscle after injection of naked DNA was shown by others to increase transgene expression. Information regarding tissue damage caused by electroporation is conflicting. It is also not well known how plasmid electroporation compares with transfection by adenoviral vectors. To investigate these questions the most used protocol for muscle electroporation was used, i.e. 8 pulses of 200 V/cm and 20 ms at a frequency of 1 Hz.
Results: Intra-muscular DNA transfer of pLuciferase was increased by 2 logs after electroporation, confirming data described by others. However, the blood levels of the encoded protein were still lower than those obtained after injection of first generation adenoviral vectors. Also, the electroporation procedure, on its own, caused severe muscle damage consisting of rhabdomyolysis and infiltration, whereas the adenoviral vectors caused only a slight infiltration. As damage of targeted tissue may be an advantage in the case of tumour transfection, we also compared the two transfection methods in tumour tissue. In case of poorly permissive tumours, adenoviral vectors cannot transfect more than 2% of the tumour tissue without inducing significant liver damage. In contrast, the electroporation seems to offer a wider therapeutic window since it does not cause any systemic toxicity and still induce's significant transfection.
Conclusions: Plasmid electroporation of the muscle induce severe local damage and is of no advantage over adenoviral vectors for obtaining high blood levels of a vector encoded protein. In contrast, electroporation of tumours might be safer than adenoviral gene transfer.