Small interfering RNA (siRNA) has demonstrated significant success in treating hepatic diseases through intravenous (i.v.) or subcutaneous (s.c.) injection. In this study, we reported that siRNA encapsulated in lipid nanoparticles (termed RBP131) can effectively achieve gene silencing in the liver via the non-invasive intratracheal (i.t.) administration. Following a single i.t. dose, apolipoprotein B (ApoB) gene silencing can be sustained for over three weeks, with a remarkably low effective dose (ED₅₀) of 0.13 mg/kg. Multiple doses of 0.5 mg/kg administered twice a week can maintain long-term knockdown efficiency of around 90%. Further, in a hepatitis B virus (HBV) transgenic mouse model, significant X gene silencing (over 80%) was observed with the treatment of 1 mg/kg siHBV-RBP131 formulation, comparable to the efficacy achieved through i.v. injection. Importantly, toxicity analysis indicated that the siRNA-RBP131 formulation was well tolerated in mice, even at a high dose of 10 mg/kg (over 70-times higher than ED₅₀). These findings open a new avenue for delivering siRNA-LNPs to the liver in a noninvasive strategy, providing a more patient-friendly approach that can be more easily translated into clinical practice.

Harnessing surface engineering strategies to functionalize nucleic acid-lipid nanoparticles (LNPs) for improved performance has been a hot research topic since the approval of the first siRNA drug, patisiran, and two mRNA-based COVID-19 vaccines, BNT162b2 and mRNA-1273. Currently, efforts have been mainly made to construct targeted LNPs for organ- or cell-type-specific delivery of nucleic acid drugs by conjugation with various types of ligands. In this review, we describe the surface engineering strategies for nucleic acid-LNPs, considering ligand types, conjugation chemistries, and incorporation methods. We then outline the general purification and characterization techniques that are frequently used following the engineering step and emphasize the specific techniques for certain types of ligands. Next, we comprehensively summarize the currently accessible organs and cell types, as well as the other applications of the engineered LNPs. Finally, we provide considerations for formulating targeted LNPs and discuss the challenges of successfully translating the “proof of concept” from the laboratory into the clinic. We believe that addressing these challenges could accelerate the development of surface-engineered LNPs for targeted nucleic acid delivery and beyond.