BACKGROUND: Electroporation is a physical method used to transfer molecules into cells and tissues. Clinical applications have been developed for antitumor drug delivery. Clinical trials of gene electrotransfer are under investigation. However, knowledge about how DNA enters cells is not complete. By contrast to small molecules that have direct access to the cytoplasm, DNA forms a long lived complex with the plasma membrane and is transferred into the cytoplasm with a considerable delay. METHODS: To increase our understanding of the key step of DNA/membrane complex formation, we investigated the dependence of DNA/membrane interaction and gene expression on electric pulse polarity and repetition frequency. RESULTS: We observed that both are affected by reversing the polarity and by increasing the repetition frequency of pulses. The results obtained in the present study reveal the existence of two classes of DNA/membrane interaction: (i) a metastable DNA/membrane complex from which DNA can leave and return to external medium and (ii) a stable DNA/membrane complex, where DNA cannot be removed, even by applying electric pulses of reversed polarity. Only DNA belonging to the second class leads to effective gene expression. CONCLUSIONS: The life-time of DNA/membrane complex formation is of the order of 1 s and has to be taken into account to improve protocols of electro-mediated gene delivery. Copyright 2009 John Wiley & Sons, Ltd.
BACKGROUND: Electroporation is a physical method used to transfer molecules into cells and tissues. Clinical applications have been developed for antitumor drug delivery. Clinical trials of gene electrotransfer are under investigation. However, knowledge about how DNA enters cells is not complete. By contrast to small molecules that have direct access to the cytoplasm, DNA forms a long lived complex with the plasma membrane and is transferred into the cytoplasm with a considerable delay. METHODS: To increase our understanding of the key step of DNA/membrane complex formation, we investigated the dependence of DNA/membrane interaction and gene expression on electric pulse polarity and repetition frequency. RESULTS: We observed that both are affected by reversing the polarity and by increasing the repetition frequency of pulses. The results obtained in the present study reveal the existence of two classes of DNA/membrane interaction: (i) a metastable DNA/membrane complex from which DNA can leave and return to external medium and (ii) a stable DNA/membrane complex, where DNA cannot be removed, even by applying electric pulses of reversed polarity. Only DNA belonging to the second class leads to effective gene expression. CONCLUSIONS: The life-time of DNA/membrane complex formation is of the order of 1 s and has to be taken into account to improve protocols of electro-mediated gene delivery. Copyright 2009 John Wiley & Sons, Ltd.