Recent advances in nanoparticulate RNA delivery systems

Abstract

Nanoparticle-based RNA delivery has shown great progress in recent years with the approval of two mRNA vaccines for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) and a liver-targeted siRNA therapy. Here, we discuss the preclinical and clinical advancement of new generations of RNA delivery therapies along multiple axes. Improvements in cargo design such as RNA circularization and data-driven untranslated region optimization can drive better mRNA expression. New materials discovery research has driven improved delivery to extrahepatic targets such as the lung and splenic immune cells, which could lead to pulmonary gene therapy and better cancer vaccines, respectively. Other organs and even specific cell types can be targeted for delivery via conjugation of small molecule ligands, antibodies, or peptides to RNA delivery nanoparticles. Moreover, the immune response to any RNA delivery nanoparticle plays a crucial role in determining efficacy. Targeting increased immunogenicity without induction of reactogenic side effects is crucial for vaccines, while minimization of immune response is important for gene therapies. New developments have addressed each of these priorities. Last, we discuss the range of RNA delivery clinical trials targeting diverse organs, cell types, and diseases and suggest some key advances that may play a role in the next wave of therapies.

Fig. 1.

(A) Overview of nanoparticle RNA delivery. RNA must be encapsulated in the nanoparticle, endocytosed, and escape the endosome into the cytoplasm. Generated by BioRender.com. (B) Sample of polymeric and lipid-based RNA nanoparticle delivery materials, lipid tails in red and cationic or ionizable components in blue. R groups for charge-altering releasable transporters (CARTs) and poly(beta-amino ester) PBAEs indicate structural flexibility that can be tuned via high-throughput screening; for cell-penetrating peptides (CPPs), structural optionality is not explicitly shown, but hundreds of CPPs for delivery of various cargos have been described (25). Lipid-based delivery can use ionizable lipid-free lipoplexes, such as those containing DOTMA and DOPE, while LNPs contain ionizable lipids with examples given here. DLin-MD3-DMA is FDA approved in a liver siRNA delivery formulation, and SM-102 and ALC-0315 are used in the Moderna and Pfizer-BioNTech COVID mRNA vaccines, respectively. OF-02 is highly potent for liver mRNA delivery lipid and illustrates the structural diversity of ionizable lipids.

Fig. 2.

(A) Present and future delivery material discovery strategies. Black ellipses represent ionizable lipid screening efforts with size of ellipse representing the number of lipids screened. (i) Small, targeted, rationally designed screen. (ii) High-throughput screen. (iii) High-throughput machine learning–guided screen. (iv) Small, targeted machine learning–guided screen. (B) The components of an LNP. (C) Prominent multicomponent reactions used to generate ionizable lipid libraries; Michael addition can use an acrylate or acrylamide. (D) Barcoded delivery screening. (E) RNA delivery nanoparticles can be targeted to specific cell types via (i) incorporation of specific ligands, (ii) antibody conjugation, or (iii) peptide conjugation.