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Title: Understanding structure-activity relationships of pH-sensitive cationic lipids facilitates the rational identification of promising lipid nanoparticles for delivering siRNAs in vivo. Author: Sato Y, Hashiba K, Sasaki K, Maeki M, Tokeshi M, Harashima H. Journal: J Control Release; 2019 Feb 10; 295():140-152. PubMed ID: 30610950. Abstract: Lipid nanoparticles (LNPs) are one of the more promising technologies for efficiently delivering short interfering RNA (siRNA) in vivo. A pH-sensitive cationic lipid that facilitates the targeting of hepatocytes and endosomal escape, strongly influences the availability of siRNA, thus making it a key material for efficient siRNA delivery. A systematic knowledge regarding lipid structure-activity relationships would greatly facilitate the development of sophisticated pH-sensitive cationic lipids for use in siRNA-based therapeutics. The systemic derivatization of a hydrophilic head group and hydrophobic tails of YSK12-C4, a pH-sensitive cationic lipid that was developed in our laboratory, revealed that hydrophilic head significantly affected the apparent pKa of the final product, a key factor in both intrahepatic distribution and endosomal escape. The clogP value of a hydrophilic head group was found to be associated with the apparent pKa of the product. In contrast, the hydrophobic tail structure strongly affected intrahepatic distribution without depending on apparent pKa. A structure-activity relationship study enabled the selection of an adequate combination of a hydrophilic head group and hydrophobic tails and permitted a potent LNP composed of a pH-sensitive cationic lipid CL4H6 (CL4H6-LNPs) to be developed that showed efficient gene silencing activity (50% effective dose: 0.0025 mg/kg), biodegradability and was tolerated. In vivo experiments revealed that the CL4H6-LNPs showed a superior efficiency for endosomal escape, cytosolic release and the RNA-induced silencing for the complex-loading of siRNAs compared to the previously developed LNPs.[Abstract] [Full Text] [Related] [New Search]