Nucleoside-modified messenger RNA

A nucleoside-modified messenger RNA (modRNA) is a synthetic messenger RNA (mRNA) in which some nucleosides are replaced by other naturally modified nucleosides or by synthetic nucleoside analogues.[1] modRNA is used to induce the production of a desired protein in certain cells. An important application is the development of mRNA vaccines, of which the first authorized were COVID-19 vaccines (such as Comirnaty and Spikevax).

BackgroundEdit

 
A ribosome (depicted in green) creates a protein (depicted here as a string of beads representing amino acids) encoded in an mRNA (depicted as a ribbon of nucleotides) that may be modified to reduce inflammation in the cell.

mRNA is produced by synthesising a ribonucleic acid (RNA) strand from nucleotide building blocks according to a deoxyribonucleic acid (DNA) template, a process that is called transcription.[2] When the building blocks provided to the RNA polymerase include non-standard nucleosides such as pseudouridine — instead of the standard adenosine, cytidine, guanosine, and uridine nucleosides — the resulting mRNA is described as nucleoside-modified.[3]

Production of protein begins with assembly of ribosomes on the mRNA, the latter then serving as a blueprint for the synthesis of proteins by specifying their amino acid sequence based on the genetic code in the process of protein biosynthesis called translation.[4]

OverviewEdit

To induce cells to make proteins that they do not normally produce, it is possible to introduce heterologous mRNA into the cytoplasm of the cell, bypassing the need for transcription. In other words, a blueprint for foreign proteins is "smuggled" into the cells. To achieve this goal, however, one must bypass cellular systems that prevent the penetration and translation of foreign mRNA. There are nearly-ubiquitous enzymes called ribonucleases (also called RNAses) that break down unprotected mRNA.[5] There are also intracellular barriers against foreign mRNA, such as innate immune system receptors, toll-like receptor (TLR) 7 and TLR8, located in endosomal membranes. RNA sensors like TLR7 and TLR8 can dramatically reduce protein synthesis in the cell, trigger release of cytokines such as interferon and TNF-alpha, and when sufficiently intense lead to programmed cell death.[6]

The inflammatory nature of exogenous RNA can be masked by modifying the nucleosides in mRNA.[7] For example, uridine can be replaced with a similar nucleoside such as pseudouridine (Ψ) or N1-methyl-pseudouridine (m1Ψ),[8] and cytosine can be replaced by 5-methylcytosine.[9] Some of these, such as pseudouridine and 5-methylcytosine, occur naturally in eukaryotes.[10] Inclusion of these modified nucleosides alters the secondary structure of the mRNA, which can reduce recognition by the innate immune system while still allowing effective translation.[9]

Significance of untranslated regionsEdit

A normal mRNA starts and ends with sections that do not code for amino acids of the actual protein. These sequences at the 5′ and 3′ ends of an mRNA strand are called untranslated regions (UTRs). The two UTRs at their strand ends are essential for the stability of an mRNA and also of a modRNA as well as for the efficiency of translation, i.e. for the amount of protein produced. By selecting suitable UTRs during the synthesis of a modRNA, the production of the target protein in the target cells can be optimised.[5][11]

DeliveryEdit

 
Comparing uptake of RNA and modRNA by the cell

Various difficulties are involved in the introduction of modRNA into certain target cells. First, the modRNA must be protected from ribonucleases.[5] This can be accomplished, for example, by wrapping it in liposomes. Such "packaging" can also help to ensure that the modRNA is absorbed into the target cells. This is useful, for example, when used in vaccines, as nanoparticles are taken up by dendritic cells and macrophages, both of which play an important role in activating the immune system.[12]

Furthermore, it may be desirable that the modRNA applied is introduced into specific body cells. This is the case, for example, if heart muscle cells are to be stimulated to multiply. In this case, the packaged modRNA can be injected directly into an artery such as a coronary artery.[13]

ApplicationsEdit

An important field of application are mRNA vaccines, of which the first authorized for use in humans were COVID-19 vaccines to address SARS-CoV-2.[14][15][16][17][18][19][20] Examples of COVID-19 vaccines using modRNA include those developed by the cooperation of BioNTech/Pfizer/Fosun International (BNT162b2), and by Moderna (mRNA-1273).[21][22][23] The zorecimeran vaccine developed by Curevac, however, uses unmodified RNA.[24]

Other possible uses of modRNA include the regeneration of damaged heart muscle tissue[25][26] and cancer therapy.[27][28]

ReferencesEdit

  1. ^ Chien KR, Zangi L, Lui KO (October 2014). "Synthetic chemically modified mRNA (modRNA): toward a new technology platform for cardiovascular biology and medicine". Cold Spring Harbor Perspectives in Medicine. 5 (1): a014035. doi:10.1101/cshperspect.a014035. PMC 4292072. PMID 25301935.
  2. ^ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). From DNA to RNA (4 ed.). Garland Science.
  3. ^ Pardi N, Weissman D (2017). "Nucleoside Modified mRNA Vaccines for Infectious Diseases". RNA Vaccines. Methods in Molecular Biology. 1499. Clifton, N.J. pp. 109–121. doi:10.1007/978-1-4939-6481-9_6. ISBN 978-1-4939-6479-6. PMID 27987145.
  4. ^ Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J (2000). The Three Roles of RNA in Protein Synthesis (4th ed.). New York: W. H. Freeman. pp. Sec 4.4.
  5. ^ a b c Schlake T, Thess A, Fotin-Mleczek M, Kallen KJ (November 2012). "Developing mRNA-vaccine technologies". RNA Biology. 9 (11): 1319–30. doi:10.4161/rna.22269. PMC 3597572. PMID 23064118.
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  7. ^ Karikó, K; Buckstein, M; Ni, H; Weissman, D (August 2005). "Suppression of RNA recognition by Toll-like receptors: the impact of nucleoside modification and the evolutionary origin of RNA". Immunity. 23 (2): 165–75. doi:10.1016/j.immuni.2005.06.008. PMID 16111635.
  8. ^ Andries O, Mc Cafferty S, De Smedt SC, Weiss R, Sanders NN, Kitada T (2015). "N1-methylpseudouridine-incorporated mRNA outperforms pseudouridine-incorporated mRNA by providing enhanced protein expression and reduced immunogenicity in mammalian cell lines and mice". Journal of Controlled Release. 217: 337–344. doi:10.1016/j.jconrel.2015.08.051. hdl:1854/LU-6993270. PMID 26342664.
  9. ^ a b Svitkin YV, Cheng YM, Chakraborty T, Presnyak V, John M, Sonenberg N (June 2017). "N1-methyl-pseudouridine in mRNA enhances translation through eIF2α-dependent and independent mechanisms by increasing ribosome density". Nucleic Acids Research. 45 (10): 6023–6036. doi:10.1093/nar/gkx135. PMC 5449617. PMID 28334758.
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  11. ^ Orlandini von Niessen AG, Poleganov MA, Rechner C, Plaschke A, Kranz LM, Fesser S, et al. (April 2019). "Improving mRNA-Based Therapeutic Gene Delivery by Expression-Augmenting 3' UTRs Identified by Cellular Library Screening". Molecular Therapy. 27 (4): 824–836. doi:10.1016/j.ymthe.2018.12.011. PMC 6453560. PMID 30638957.
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  13. ^ Carlsson L, Clarke JC, Yen C, Gregoire F, Albery T, Billger M, et al. (June 2018). "VEGF-A mRNA Improves Cardiac Function after Intracardiac Injection 1 Week Post-myocardial Infarction in Swine". Molecular Therapy. Methods & Clinical Development. 9: 330–346. doi:10.1016/j.omtm.2018.04.003. PMC 6054703. PMID 30038937.
  14. ^ "Pfizer and BioNTech Celebrate Historic First Authorization in the U.S. of Vaccine to Prevent COVID-19". www.businesswire.com. 12 December 2020.
  15. ^ Polack FP, Thomas SJ, Kitchin N, Absalon J, Gurtman A, Lockhart S, et al. (December 2020). "Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine". The New England Journal of Medicine. 383 (27): 2603–2615. doi:10.1056/NEJMoa2034577. PMC 7745181. PMID 33301246. S2CID 228087117.
  16. ^ Hohmann-Jeddi C (2020-11-10). "Hoffnungsträger BNT162b2: Wie funktionieren mRNA-Impfstoffe?". Pharmazeutische Zeitung (in German). Retrieved 2020-11-28.
  17. ^ Abbasi J (September 2020). "COVID-19 and mRNA Vaccines-First Large Test for a New Approach". JAMA. 324 (12): 1125–1127. doi:10.1001/jama.2020.16866. PMID 32880613. S2CID 221476409.
  18. ^ Vogel A, Kanevsky I, Che Y, Swanson K, Muik A, Vormehr M, et al. (8 September 2020). "A prefusion SARS-CoV-2 spike RNA vaccine is highly immunogenic and prevents lung infection in non-human primates" (PDF). bioRxiv. doi:10.1101/2020.09.08.280818. S2CID 221589144.
  19. ^ "Conditions of Authorisation for Pfizer/BioNTech COVID-19 Vaccine" (Decision). Medicines & Healthcare Products Regulatory Agency. 8 December 2020.
  20. ^ Office of the Commissioner (14 December 2020). "Pfizer-BioNTech COVID-19 Vaccine". www.fda.gov (Decision). US FDA.
  21. ^ Krammer F (October 2020). "SARS-CoV-2 vaccines in development". Nature. 586 (7830): 516–527. Bibcode:2020Natur.586..516K. doi:10.1038/s41586-020-2798-3. PMID 32967006. S2CID 221887746.
  22. ^ "Moderna's Pipeline". Moderna. Retrieved 2020-11-28.
  23. ^ Dolgin, Elie (2020-11-25). "COVID-19 vaccines poised for launch, but impact on pandemic unclear". Nature Biotechnology: d41587–020–00022-y. doi:10.1038/d41587-020-00022-y. PMID 33239758. S2CID 227176634.
  24. ^ "COVID-19". CureVac. Retrieved 2020-12-21.
  25. ^ Kaur K, Zangi L (December 2020). "Modified mRNA as a Therapeutic Tool for the Heart". Cardiovascular Drugs and Therapy. 34 (6): 871–880. doi:10.1007/s10557-020-07051-4. PMC 7441140. PMID 32822006.
  26. ^ Zangi L, Lui KO, von Gise A, Ma Q, Ebina W, Ptaszek LM, et al. (October 2013). "Modified mRNA directs the fate of heart progenitor cells and induces vascular regeneration after myocardial infarction". Nature Biotechnology. 31 (10): 898–907. doi:10.1038/nbt.2682. PMC 4058317. PMID 24013197.
  27. ^ McNamara, Megan A.; Nair, Smita K.; Holl, Eda K. (2015). "RNA-Based Vaccines in Cancer Immunotherapy". Journal of Immunology Research. 2015: 794528. doi:10.1155/2015/794528. PMC 4668311. PMID 26665011.
  28. ^ Verbeke, R; Lentacker, I; Wayteck, L; Breckpot, K; Van Bockstal, M; Descamps, B; Vanhove, C; De Smedt, SC; Dewitte, H (28 November 2017). "Co-delivery of nucleoside-modified mRNA and TLR agonists for cancer immunotherapy: Restoring the immunogenicity of immunosilent mRNA". Journal of Controlled Release. 266: 287–300. doi:10.1016/j.jconrel.2017.09.041. PMID 28987878. S2CID 20794075.

Further readingEdit