Release date:2022/10/14 16:48:16

The use of synthetic oligonucleotides to alter protein expression by Watson-Crick hybridization of RNA was first described by Zamecnik and Stephenson in 1978. On this basis, after years of research on nucleic acid medicinal chemistry, RNA-targeted drugs (RTD) have become a very active field of drug design and development in the pharmaceutical industry. However, due to the instability of bare RNA and the existence of biological barriers to RNA entry into cells, achieving widespread application of RNA therapeutics in the clinic remains extremely challenging. Despite the difficulties in developing RNA-based therapies, scientists have explored a variety of techniques to promote RNA intracellular transport and metabolic stability. Here, we will summarize the current innovative developments and emerging technologies in RNA-based therapeutics.

 Major developments in the field of RNA targeting

Figure 1 Major developments in the field of RNA targeting [1]

Types and Modes of Action of RNA Therapies

1.Antisense Oligonucleotide (ASO)

Antisense Oligonucleotide (ASO) is a single-stranded oligonucleotide molecule that binds to target mRNA intracellularly via the Watson-Crick base pairing principle. ASO mainly regulates the expression of target genes through two mechanisms: ① After binding to target mRNA, ASO promotes mRNA degradation under the action of Rnase H1 (the main way) or ribozyme, thus inhibiting protein expression. This mechanism is also known as enzymatic RNA degradation; ②ASO controls the expression of target proteins by changing the splicing pattern of RNA without the help of specific enzymes, which is also known as the steric mechanism.

2. RNA interference (RNAi)

RNAi therapies use the principle of gene silencing and can be further classified as therapeutic agents using small interfering RNA (siRNA) or microRNA (miRNA). Double-stranded siRNA molecules recruit RISC to mRNA by the Watson-Crick base pairing principle to inhibit protein translation. miRNAs are single-stranded noncoding RNAs that cause mRNA translational repression or degradation in the silencing complex miRISC they induce by base-pairing with a specific RNA sequence (usually the 3'UTR).

3. CRISPR-based genome editing

The prokaryotic-derived CRISPR-associated protein (Cas) system has been widely used in mammalian cells and organisms. In this system, Cas protein and sgRNA combine to form a complex to recognize and cleave target sequences for precise and efficient genome editing.

4. Aptamer

Aptamer is a structured oligonucleotide sequence that specifically binds and inhibits protein expression. It is usually obtained by SELEX, an in vitro screening technique. They are also known as chemical antibodies because they are synthesized in a similar way to antibodies. Aptamer-based therapies mainly include: ① using Aptamer to disrupt the interaction between disease-related targets; ② using cell-specific Aptamer as a carrier to deliver other therapeutic agents to target cells or target tissues.

5. mRNA drugs

The concept of mRNA-encoded drugs was proposed in 1990 [1], when in vitro synthesized (IVT) mRNA was directly injected into mouse skeletal muscle, and the protein encoded by IVT was found to be expressed in skeletal muscle. Preclinical studies of IVT mRNA have facilitated the clinical development of mRNA vaccines. mRNA vaccines are delivered to host cells and translated into targeted antigens that activate the body's immune response. It shows great potential in the treatment of cancer and infectious diseases.

 Mechanisms of action of various RNA therapies

Figure 2. Mechanisms of action of various RNA therapies

Chemical modification of RNA drugs

ASO and siRNA are chemically modified mainly at the phosphate backbone, ribose ring, 3'- and 5' -ends to improve their substrate specificity and nuclease resistance, and to reduce their toxicity and immunogenicity. For example, siRNA 2'-F and 2'-O-Me modifications can help antagonize RNases and prevent siRNAs from activating innate immune receptors (TLR, MDA-5, and RIG-I). 5 'cap structure, ORF, flanking 5' 3 '-UTRs, 3' -poly (A) tail were optimized to enhance the translation ability of RNA through sequence optimization, nucleoside modification or sequence replacement of UTR. 5 'cap structure, ORF, flanking 5' 3 '-UTRs, 3' -poly (A) tail were optimized to enhance the translation ability of RNA through sequence optimization, nucleoside modification or sequence replacement of UTR.

Common chemical modifications of RNA drugs

Figure 3 Common chemical modifications of RNA drugs

Application of nanoparticle drug delivery system in RNA therapy

Since therapeutic RNAs carry a large number of negative charges and chemical modifications, it is necessary to develop an effective vector to protect RNA from the physiological environment [3].

1. Lipid Nanoparticles (LNPs)

Lipid nanoparticles (LNPs) are the most widely used carriers for the delivery of oligonucleotide drugs. FDA-approved LNPs contain four basic components: cationic or ionized lipids, cholesterol, helper lipids, and PEG-lipids. Selective organ targeting (SORT) technology can specifically target liver and extrahepatic tissues (lung and spleen) by adding SORT molecules to LNPs. This technology enables mRNA delivery and CRISPR-Cas gene editing in specific tissues [4].

  Structure of lipid nanoparticles

Figure 4 Structure of lipid nanoparticles

2. Polymer nanoparticles

Polyethylenimine (PEI) polymer family is the most widely studied polymer materials for nucleic acid delivery. They are composed of linear or branched polycations that can form nanoscale complexes with miRNA or siRNA. The commercially available linear PEI derivative jetPEI™ is widely used for DNA, siRNA and mRNA transfection. PBAE polymers have better biodegradability and lower cytotoxicity. Recently, researchers have used PBAE-based polymers to deliver Cas13a mRNA into the respiratory tract of mice by aerosolization for the treatment of SARS-Cov-2 [5] .

 Structure of polymer nanoparticles

Figure 5 Structure of polymer nanoparticles

FDA-Approved RNA Therapies

Fomivirsen is the first ASO drug approved by the FDA for the treatment of cytomegalovirus retinitis in AIDS patients. Mipomersen and Inotersen are second-generation ASO drugs that mediate the degradation of ApoB and TTR mRNA, respectively.

GalNAc-siRNA is a single conjugate formed by carbohydrates and siRNA, which can be used to treat various diseases only by changing the siRNA sequence. Currently, the FDA has approved GalNAc-siRNA in combination with Givosiran for the treatment of acute intermittent hepatic porphyria (AHP) and Lumasiran in the treatment of primary hyperoxaluria type 1 (PH1).

Pegaptanib is the first FDA-approved Aptamer drug targeting VEGF for the treatment of age-related macular degeneration.

During the COVID-19 epidemic, mRNA vaccines have been shown to be effective against SARS-CoV-2. Pfizer – BioNTech’s vaccine BNT162b2 (Comirnaty®) and Moderna’s vaccine mRNA-1273 are two FDA-approved SARS-CoV-2 vaccines with >94% efficacy in Phase III clinical trials.


The emerging applications of RNA drugs in modulating immune responses and the expression of disease-related proteins have provided new ideas for biomedical research. While small molecules and antibody drugs target only 0.05% of the human genome, RNA selectively acts on proteins, transcripts, and genes, thereby broadening the range of drug targets. Combining RNA chemical modifications with nanocarrier systems can improve the efficiency of RNA drug delivery. In the future, with the continuous progress of medical science and technology, RNA-based therapeutic methods are expected to be more diversified.

As a reliable worldwide supplier of PEG & ADC linkers, Biopharma PEG can provide high purity PEG derivatives in GMP and non-GMP grades for your research of lipid nanoparticles for drug delivery. We can also supply some PEG products as ingredients used in COVID-19 vaccines. For more information, please visit website at PEGs for COVID-19 vaccines.


[1]. Zhu Yiran,Zhu Liyuan,Wang Xian et al.
RNA-based therapeutics: an overview and prospectus.[J] .Cell Death Dis, 2022, 13: 644.
[2]. Wolff J A,Malone R W,Williams P et al.
Direct gene transfer into mouse muscle in vivo.[J] .Science, 1990, 247: 1465-8.
[3]. Paunovska Kalina,Loughrey David,Dahlman James E,
Drug delivery systems for RNA therapeutics.[J] .Nat Rev Genet, 2022, 23: 265-280.
[4]. Dilliard Sean A,Cheng Qiang,Siegwart Daniel J,
On the mechanism of tissue-specific mRNA delivery by selective organ targeting nanoparticles.[J] .Proc Natl Acad Sci U S A, 2021, 118: undefined.
[5]. Blanchard Emmeline L,Vanover Daryll,Bawage Swapnil Subhash et al.
Treatment of influenza and SARS-CoV-2 infections via mRNA-encoded Cas13a in rodents.[J] .Nat Biotechnol, 2021, 39: 717-726.

Related articles:
Future Perspective of PROTAC Combined With CRISPR In Anti-ancer Area
[2]. Lipid Nanoparticles for Drug and Vaccine Delivery
[3]. COVID-19 mRNA Vaccine Excipients - PEG Products Supply
[4]. Overview of mRNA-Lipid Nanoparticle COVID-19 Vaccines
[5]. Oligonucleotide Drugs: Current Status and Challenges

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