Ionization Behavior of Amino Lipids for siRNA Delivery: Determination of Ionization Constants, SAR, and the Impact of Lipid pKa on Cationic Lipid鈭払iomembrane Interactions

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• 作者：Jingtao Zhang ; Haihong Fan ; Dorothy A. Levorse ; Louis S. Crocker
• 刊名：Langmuir
• 出版年：2011
• 出版时间：March 1, 2011
• 年：2011
• 卷：27
• 期：5
• 页码：1907-1914
• 全文大小：854K
• 年卷期：v.27,no.5(March 1, 2011)
• ISSN：1520-5827

文摘

Ionizable amino lipids are being pursued as an important class of materials for delivering small interfering RNA (siRNA) therapeutics, and research is being conducted to elucidate the structure鈭抋ctivity relationships (SAR) of these lipids. The pK_a of cationic lipid headgroups is one of the critical physiochemical properties of interest due to the strong impact of lipid ionization on the assembly and performance of these lipids. This research focused on developing approaches that permit the rapid determination of the relevant pK_a of the ionizable amino lipids. Two distinct approaches were investigated: (1) potentiometric titration of amino lipids dissolved in neutral surfactant micelles; and (2) pH-dependent partitioning of a fluorescent dye to cationic liposomes formulated from amino lipids. Using the approaches developed here, the pK_a values of cationic lipids with distinct headgroups were measured and found to be significantly lower than calculated values. It was also found that lipid鈭抣ipid interaction has a strong impact on the pK_a values of lipids. Lysis of model biomembranes by cationic lipids was used to evaluate the impact of lipid pK_a on the interaction between cationic lipids and cell membranes. It was found that cationic lipid鈭抌iomembrane interaction depends strongly on lipid pK_a and solution pH, and this interaction is much stronger when amino lipids are highly charged. The presence of an optimal pK_a range of ionizable amino lipids for siRNA delivery was suggested based on these results. The pK_a methods reported here can be used to support the SAR screen of cationic lipids for siRNA delivery, and the information revealed through studying the impact of pK_a on the interaction between cationic lipids and cell membranes will contribute significantly to the design of more efficient siRNA delivery vehicles.