Advances in the delivery of RNA therapeutics: from concept to clinical reality

Abstract

The rapid expansion of the available genomic data continues to greatly impact biomedical science and medicine. Fulfilling the clinical potential of genetic discoveries requires the development of therapeutics that can specifically modulate the expression of disease-relevant genes. RNA-based drugs, including short interfering RNAs and antisense oligonucleotides, are particularly promising examples of this newer class of biologics. For over two decades, researchers have been trying to overcome major challenges for utilizing such RNAs in a therapeutic context, including intracellular delivery, stability, and immune response activation. This research is finally beginning to bear fruit as the first RNA drugs gain FDA approval and more advance to the final phases of clinical trials. Furthermore, the recent advent of CRISPR, an RNA-guided gene-editing technology, as well as new strides in the delivery of messenger RNA transcribed in vitro, have triggered a major expansion of the RNA-therapeutics field. In this review, we discuss the challenges for clinical translation of RNA-based therapeutics, with an emphasis on recent advances in delivery technologies, and present an overview of the applications of RNA-based drugs for modulation of gene/protein expression and genome editing that are currently being investigated both in the laboratory as well as in the clinic.

Keywords: Antisense oligonucleotide; CRISPR; Clinical trial; Gene editing; Gene therapy; Messenger RNA delivery; RNA nanoparticle; Short interfering RNA delivery; mRNA vaccine.

Fig. 1

Common delivery modalities for RNA. a Schematic depicting polymeric nanoparticles comprising RNA and cationic polymer. b Schematic depicting lipid nanoparticles containing RNA, a cationic/ionizable lipid, and other hydrophobic moieties (such as cholesterol) commonly used in nanoparticle formulation. c Chemical structure of a tertiary conjugate between N-acetylgalactosamine (GalNAc) and RNA that is currently in clinical trials [38]. d Examples of base, sugar, and linker modifications that have been utilized to deliver nucleic acids (modified chemistry highlighted in blue)

Fig. 2

Regulation of gene and protein expression using RNA. Once delivered into the cells, RNA macromolecules can utilize diverse intracellular mechanisms to control gene and protein expression. (I) Hybridization of antisense oligonucleotides (ASOs) to a target mRNA can result in specific inhibition of gene expression by induction of RNase H endonuclease activity, which cleaves the mRNA–ASO heteroduplex. (II) Short interfering RNA (siRNA) is recognized by the RNA-induced silencing complex (RISC), which, guided by an antisense strand of the siRNA, specifically binds and cleaves target mRNA. (III) In vitro transcribed mRNA utilizes the protein synthesis machinery of host cells to translate the encoded genetic information into a protein. Ribosome subunits are recruited to mRNA together with a cap and poly(A)-binding proteins, forming a translation initiation complex. (IV) In the CRISPR–Cas9 system, co-delivery of a single guide RNA (sgRNA) together with the mRNA encoding the Cas9 DNA endonuclease allows site-specific cleavage of double-stranded DNA, leading to the knockout of a target gene and its product. CRISPR, clustered regularly interspaced short palindromic repeats