RNA therapeutics
Because of its unique properties (such as its typically single-stranded nature and its 2' OH group) and its ability to adopt many different secondary/tertiary structures, both coding and noncoding RNAs have attracted attention in medicine.
[12] DNA therapeutics needs access to the nucleus to be transcribed into RNA, and its functionality depends on nuclear envelope breakdown during cell division.
[13] Moreover, unlike plasmids and viral vectors, mRNAs do not integrate into the genome and therefore do not have the risk of insertional mutagenesis,[14] making them suitable for use in cancer vaccines, tumor immunotherapy and infectious disease prevention.
[29] In 1995, Robert Conry demonstrated that intramuscular injection of naked RNA encoding carcinoembryonic antigen elicited antigen-specific antibody responses.
[34] Meanwhile, Argos Therapeutics had initiated a Phase III clinical trial using DCs with advanced renal cell carcinoma in 2015 (NCT01582672) but it was terminated due to the lack of efficacy.
It improved the translation efficiency and stability of IVT mRNA and enhanced the presentation of the mRNA-encoded antigen on MHC class I and II molecules.
[36][37] Then, they found out that the direct injection of naked IVT mRNA into lymph nodes was the most effective way to induce T cell responses.
[38] Based on this discovery, first-in-human testing of the injection of naked IVT mRNA encoding cancer antigens by BioNTech has started with patients with melanoma (NCT01684241).
[39] Recently, the new cancer immunotherapy, the combining of self-delivering RNA(sd-rxRNA) and adoptive cell transfer(ACT) therapy, was invented by RXi Pharmaceuticals and the Karolinska Institute.
There are a few phase I and II clinical trials using IVT mRNA encoding combinations and it shows that antigen-specific CD8+ and CD4+ T cell responses can be induced.
[50][51] In 2021, SLR14 was reported to prevent infection in the lower respiratory tract and severe disease in an interferon type I (IFN-I)–dependent manner in mice.
[52] A 2022 study by researchers from the Mayo Clinic, Maastricht University, and Ethris GmBH, a biotech company that focuses on RNA therapeutics, found that chemically modified mRNA encoding BMP-2 promoted dosage-dependent healing of femoral osteotomies in male rats.
Compared to receiving rhBMP-2 directly, bony tissues regenerated after mRNA treatment displayed superior strength and less formation of massive callus.
Antisense drugs are being developed to treat lung cancer, diabetes and diseases such as arthritis and asthma with a major inflammatory component.
So far, applications of antisense RNAs in antivirus and anticancer treatments and in regulating the expression of related genes in plants and microorganisms have been explored.
To improve the delivery issues, chemical modifications, and new oligonucleotide designs have been studied to enhance the drug distribution, side effects, and tolerability.
For instance, siRNA can be used to target mRNAs that code for proteins that promote tumor growth such as the VEGF receptor and telomerase enzyme.
[74] Micro RNAs (miRNAs) are short, ~19-23 base pair long RNA oligonucleotides that are involved in the microRNA-induced silencing complex.
[73] An example of one mimic miRNA therapy that demonstrated efficacy in impeding lung cancer tumor growth in mouse studies is miR-34a.
[84][85] Broadly, aptamers are small molecules composed of either single-stranded DNA or RNA and are typically 20-100 nucleotides in length,[7][8][87] or ~3-60 kDa.
[87][88] Because of their single-stranded nature, aptamers are capable of forming many secondary structures, including pseudoknots, stem loops, and bulges, through intra-strand base pairing interactions.
[7][9] Besides their strong binding ability, aptamers are also valued because they can be used on targets that are not capable of being bound by small peptides generated by phage display or by antibodies, and they are able to differentiate between conformational isomers and amino acid substitutions.
[87][90][91] Also, because aptamers are nucleic-acid based, they can be directly synthesized, eliminating the need for cell-based expression and extraction as is the case in antibody production.
[87][93] Aptamers were originally discovered in 1990 when Lary Gold and Craig Tuerk utilized a method of directed evolution known as SELEX to isolate a small single stranded RNA molecule that was capable of binding to T4 bacteriophage DNA polymerase.
[7] After subsequent removal of the non-specific aptamers, the remaining library members are then exposed to the desired target, which can be a protein, peptide, cell type, or even an organ (in the case of live animal-based SELEX).
[87] When RNA aptamers are designed to act as agonists, they promote immune cell activation as a co-stimulatory molecule, thus aiding in the mobilization of the body's own defense system.
[7][8][87] Originally approved in 2004 to treat age-related macular degeneration, Pegaptanib is a 28 nucleotide RNA aptamer that acts as a VEGF antagonist.
[8][87][88][114][115] Because of their negative charge, RNA aptamers are additionally known to bind proteins in the bloodstream, leading to non-target tissue delivery and toxicity.
For instance, a polyethylene glycol (PEG) moiety can be attached to increase the size of the aptamer, thereby preventing its removal from the bloodstream by the renal glomerulus.
[8] Nevertheless, despite these potential solutions to reduced in vivo efficacy, it is possible that chemically modifying the aptamer may weaken its binding affinity towards its target.
