Intracellular delivery of nucleic acids: Differences between transfection and sifection reflect differences between DNA and RNA, and between oligodeoxynucleotides and oligonucleotides

Abstract

4 Summary: Altogether, our study demonstrates that pDNA and siRNA formulate differently with cationic liposomes, and that mechanistically the two species of nucleic acid can vary substantially in both their intracellular up-take rates and accumulation into defined intracellular vesicles. While researchers may be able to tolerate even modest toxicity when it comes to pDNA delivery, such toxicity is completely inappropriate for siRNA delivery especially when functional genomics applications are to be considered. In this respect, CDAN/DOPE (45:55, m/m; siFECTamine) cationic liposomes appear to be an ideal starting point for functional siRNA delivery given minimal toxicity. In many ways, cationic-liposome-mediated delivery of pDNA is a mature field compared with siRNA delivery. Therefore, as with pDNA delivery before, detailed research into cationic liposome formulations and delivery conditions will be essential in order to try and understand parameters for optimal siRNA delivery involving different cell types, and different growth and handling conditions in vitro. Nonetheless, the nuclear barrier problem and the requirement for long-term expression after delivery to cells represent two enduring hurdles that cationic-liposome-mediated pDNA delivery must solve if cationic-liposome-based synthetic non-viral vector systems are to prevail as the vector systems of choice for gene therapy. By contrast, cationic liposome-mediated siRNA delivery is presented with no such hurdles, implying that cationic-liposome-based synthetic non-viral vectors systems for siRNA therapeutics may forge ahead of applications of the same for gene therapy in spite of the relative infancy of the siRNA field; but such optimism may yet have to be tempered by realism as the siRNA story unfolds!