The Limitless Future of RNA Therapeutics

Abstract

Recent advances in the generation, purification and cellular delivery of RNA have enabled development of RNA-based therapeutics for a broad array of applications. RNA therapeutics comprise a rapidly expanding category of drugs that will change the standard of care for many diseases and actualize personalized medicine. These drugs are cost effective, relatively simple to manufacture, and can target previously undruggable pathways. It is a disruptive therapeutic technology, as small biotech startups, as well as academic groups, can rapidly develop new and personalized RNA constructs. In this review we discuss general concepts of different classes of RNA-based therapeutics, including antisense oligonucleotides, aptamers, small interfering RNAs, microRNAs, and messenger RNA. Furthermore, we provide an overview of the RNA-based therapies that are currently being evaluated in clinical trials or have already received regulatory approval. The challenges and advantages associated with use of RNA-based drugs are also discussed along with various approaches for RNA delivery. In addition, we introduce a new concept of hospital-based RNA therapeutics and share our experience with establishing such a platform at Houston Methodist Hospital.

Keywords: RNA therapeutics; delivery of RNA therapeutics; hospital-based RNA therapeutics; messenger RNAs (mRNAs); self-amplifying mRNA.

FIGURE 1

Schematic illustrating different classes of RNA therapeutics. ASO, antisense oligonucleotide; RNA, ribonucleic acid; RNAi, RNA interference; siRNA, small interfering RNA; miRNA, microRNA; mRNA, messenger RNA; A, adenosine molecule; AAAAA, poly A tail.

FIGURE 2

Schematic illustrating the mode of action of an antisense drug to treat spinal muscular atrophy. The antisense drugs reach nucleus, displace hnRNP proteins and increase the synthesis of transcripts containing exon 7 and thereby generate full length SMN protein (Rigo et al., 2012). SMN, survival of motor neuron; hnRNP, heterogeneous nuclear ribonucleoprotein; pre-mRNA, precursor mRNA; mRNA, messenger RNA; RNA, ribonucleic acid.

FIGURE 3

Schematic illustrating the mechanism of action of small interfering RNA (siRNA) drug, patisiran. The drugs are encapsulated in lipid nanoparticles and administered intravenously. After administration, the drugs finally reach hepatocyte and released into the cytoplasm, where it is loaded onto the RISC. The antisense strand hybridizes with target mRNA to suppress the production of target protein (TTR) (Kristen et al., 2018). TTR, transthyretin; wt, wild type; RISC, RNA-induced silencing complex; mRNA, messenger RNA; RNA, ribonucleic acid.

FIGURE 4

Schematic illustrating the sequence of pegaptanib with its secondary structure. PEG, polyethylene glycol; dT, deoxthymidine (Ng et al., 2006; Amadio et al., 2016).

FIGURE 5

Schematic illustration of intravenous administration of mRNA encapsulated in lipid nanoparticles (LNP) to restore missing/defective protein in hepatic cells (An et al., 2017). mRNA, messenger RNA; RNA, ribonucleic acid.

FIGURE 6

Schematic showing the mechanism of action of conventional (BioNTech and Moderna COVID-19 vaccines) and self-amplifying mRNA vaccines. The mRNA vaccine is translated into protein, processed by antigen presenting cells, and subsequently activates immune responses. nsP, non-structural protein; Cap, N7-methylated guanosine structure covalently joined to the first nucleotide of the mRNA through a reverse 5′ to 5′ triphosphate linkage (Kowalski et al., 2019; Dolgin, 2021); A, adenosine molecule; (A)n, poly-A tail; UTR, untranslated region.

FIGURE 7

Schematic illustrations of the use of mRNA in engineering cells ex vivo. T cells derived from peripheral blood of patients suffering from disease are modified ex vivo with mRNA expressing the chimeric antigen receptor (CAR) and then modified cells are reinfused into the patient (Bertoletti and Tan, 2020). mRNA, messenger RNA; RNA, ribonucleic acid.

FIGURE 8

Lipid based nanoparticles accommodate a variety of therapeutic payloads including hydrophobic and hydrophilic small molecules, genetic materials, and proteins. One of the advantages of this platform is its ability to functionalize the surface with various proteins that can serve to target and localize nanoparticles over specific targets, imaging probes or covalent modification (Sushnitha et al., 2020; Zinger et al., 2020).

FIGURE 9

Biomimetic Nanoparticles – “Leukosome” Technology. Biomimetic nanoparticles developed by Molinaro et al. (2016) “Leukosomes.” The composition of these particles consists of a liposome together with proteins derived from leukocytes. These particles preferentially adhere to activated endothelium at sites of inflammation, and have intrinsic anti-inflammatory properties.

FIGURE 10

Hospital-based RNA therapeutics (TX) program in Houston Methodist. CMO, contract manufacturing organization; GLP, good laboratory practice; cGMP, current good manufacturing practice.