Ionizable Cholesterol‐Integrated Lipid Nanoparticles for Efficient siRNA Delivery to Solid Tumors

Lipid nanoparticles (LNPs) are clinically validated platform for the delivery of small interfering RNA (siRNA) therapeutics. However, conventional LNPs typically consist of multiple lipid components, which complicates formulation optimization and limits compositional flexibility. Furthermore, efficient delivery of siRNA to extrahepatic tissues, including solid tumors, remains a major challenge. To address these limitations, we developed a class of ionizable cholesterol derivatives by conjugating biocompatible dimethylated amino acids to cholesterol through a cleavable linker, thereby integrating the structural role of cholesterol and the pH-responsive ionization of ionizable lipids into a single molecule. Five i-Chol derivatives were synthesized and formulated into LNPs, which demonstrated efficient siRNA encapsulation and delivery in cancer cells. The resulting siRNA@i-Chol LNPs exhibited uniform particle size and near-neutral surface charge, indicating favorable physicochemical properties for systemic administration. Notably, phenylalanine-based cholesterol LNPs (Phe-Chol LNPs) loaded with siRNA targeting kinesin spindle protein (KIF11) achieved the most potent in vitro gene knockdown in PC3 prostate cancer cells and induced significant dose-dependent antitumor activity in a xenograft model without observable systemic toxicity. Collectively, this study establishes a simplified i-Chol LNP platform that maintains high siRNA delivery efficiency to solid tumors and provides a versatile framework for further LNP engineering and scalable manufacturing.