Transfection Activity of Binary Mixtures of Cationic
O-Substituted Phosphatidylcholine Derivatives: The
Hydrophobic Core Strongly Modulates Their Physical
Properties and DNA Delivery Efficacy
Li Wang 1, Rumiana Koynova 1, Harsh R. Parikh 1 and Robert C. MacDonald 1*
1 Northwestern University
* To whom correspondence should be addressed. E-mail: macd{at}northwestern.edu.
Submitted on July 5, 2006
Revised on July 25, 2006
Accepted on 8 August 2006
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Abstract |
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A combination of two cationic lipid derivatives having the same head group but tails of different chain lengths has been shown to have considerably different transfection activity than do the separate molecules. Such findings point to the importance of investigating the hydrophobic portions of cationic amphiphiles. Hence, we have synthesized a variety of cationic phosphatidylcholines with unusual hydrophobic moieties and have evaluated their transfection activity and that of their mixtures with the original molecule of this class, dioleoyl-O-ethylphosphatidylcholine (EDOPC). Four distinct relationships between transfection activity and composition of the mixture(plotted as percent of the new compound added to EDOPC)were found, namely, with a maximum or minimum, with a proportional change or with essentially no change. Relevant physical properties of the lipoplexes were also examined; specifically, membrane fusion (by fluorescence resonance energy transfer between cationic and anionic lipids) and DNA unbinding (measured both as accessibility of DNA to EtBr by electrophoresis and by fluorescence resonance energy transfer between DNA and cationic lipid), both following the addition of negatively charged membrane lipids. Fusibility increased with increasing content of second cationic lipid, regardless of the transfection pattern. However, the extent of DNA unbinding following addition of negatively charged membrane lipids did correlate with extent of transfection. The phase behavior of cationic lipids per se as well as that of their mixtures with membrane lipids revealed structural differences that may account for and support the hypothesis that a membrane lipid-triggered, lamellar-->non-lamellar phase transition that facilitates DNA release is critical to efficient transfection by cationic lipids
Key Words:
EDOPC, cationic lipid, cationic lipoid, lipid transfection, non-lamellar phase
