Department of Pharmaceutical Sciences, Merck Research Laboratories, Merck & Co., Inc., West Point, Pennsylvania, USA.
Langmuir. 2011 Aug 2;27(15):9473-83. doi: 10.1021/la201464k. Epub 2011 Jun 29.
Delivery of siRNA is a major obstacle to the advancement of RNAi as a novel therapeutic modality. Lipid nanoparticles (LNP) consisting of ionizable amino lipids are being developed as an important delivery platform for siRNAs, and significant efforts are being made to understand the structure-activity relationship (SAR) of the lipids. This article uses a combination of small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) to evaluate the interaction between cholesterol-conjugated ionizable amino lipids and biomembranes, focusing on an important area of lipid SAR--the ability of lipids to destabilize membrane bilayer structures and facilitate endosomal escape. In this study, cholesterol-conjugated amino lipids were found to be effective in increasing the order of biomembranes and also highly effective in inducing phase changes in biological membranes in vitro (i.e., the lamellar to inverted hexagonal phase transition). The phase transition temperatures, determined using SAXS and DSC, serve as an indicator for ranking the potency of lipids to destabilize endosomal membranes. It was found that the bilayer disruption ability of amino lipids depends strongly on the amino lipid concentration in membranes. Amino lipids with systematic variations in headgroups, the extent of ionization, tail length, the degree of unsaturation, and tail asymmetry were evaluated for their bilayer disruption ability to establish SAR. Overall, it was found that the impact of these lipid structure changes on their bilayer disruption ability agrees well with the results from a conceptual molecular "shape" analysis. Implications of the findings from this study for siRNA delivery are discussed. The methods reported here can be used to support the SAR screening of cationic lipids for siRNA delivery, and the information revealed through the study of the interaction between cationic lipids and biomembranes will contribute significantly to the design of more efficient siRNA delivery vehicles.
递送 siRNA 是 RNAi 作为一种新型治疗方法的主要障碍。由可离子化氨基脂质组成的脂质纳米颗粒（LNP）被开发为 siRNA 的重要递送平台，并且正在做出重大努力来理解脂质的结构-活性关系（SAR）。本文使用小角 X 射线散射（SAXS）和差示扫描量热法（DSC）相结合的方法来评估胆固醇缀合的可离子化氨基脂质与生物膜之间的相互作用，重点关注脂质 SAR 的一个重要领域——脂质破坏双层膜结构并促进内涵体逃逸的能力。在这项研究中，发现胆固醇缀合的氨基脂质有效地增加了生物膜的有序性，并且在体外非常有效地诱导生物膜发生相变（即层状到六方相转变）。使用 SAXS 和 DSC 确定的相变温度可作为指示脂质破坏内涵体膜的效力的指标。发现氨基脂质破坏双层的能力强烈依赖于膜中氨基脂质的浓度。对具有系统变化的头基、离子化程度、尾长、不饱和程度和尾不对称性的氨基脂质进行评估，以确定其破坏双层的能力，从而建立 SAR。总体而言，发现这些脂质结构变化对其双层破坏能力的影响与概念性分子“形状”分析的结果非常吻合。讨论了该研究结果对 siRNA 递送的意义。这里报道的方法可用于支持阳离子脂质用于 siRNA 递送的 SAR 筛选，并且对阳离子脂质与生物膜之间相互作用的研究所揭示的信息将为设计更有效的 siRNA 递送载体做出重大贡献。
