Morpholino

Not to be confused with morpholine or morphine.
Segment of a Morpholino-RNA heteroduplex, 8-mer shown

A Morpholino, also known as a Morpholino oligomer and as a phosphorodiamidate Morpholino oligomer (PMO), is a type of oligomer molecule (colloquially, an oligo) used in molecular biology to modify gene expression. Its molecular structure contains DNA bases attached to a backbone of methylenemorpholine rings linked through phosphorodiamidate groups. Morpholinos block access of other molecules to small (~25 base) specific sequences of the base-pairing surfaces of ribonucleic acid (RNA). Morpholinos are used as research tools for reverse genetics by knocking down gene function.

This article discusses only the Morpholino antisense oligomers, which are nucleic acid analogs. The word "Morpholino" can occur in other chemical names, referring to chemicals containing a six-membered morpholine ring. To help avoid confusion with other morpholine-containing molecules, when describing oligos "Morpholino" is often capitalized as a trade name, but this usage is not consistent across scientific literature. Morpholino oligos are sometimes referred to as PMO (for phosphorodiamidate morpholino oligomer), especially in medical literature. Vivo-Morpholinos and PPMO are modified forms of Morpholinos with chemical groups covalently attached to facilitate entry into cells.

Gene knockdown is achieved by reducing the expression of a particular gene in a cell. In the case of protein-coding genes, this usually leads to a reduction in the quantity of the corresponding protein in the cell. Knocking down gene expression is a method for learning about the function of a particular protein; in a similar manner, causing a specific exon to be spliced out of the RNA transcript encoding a protein can help to determine the function of the protein moiety encoded by that exon or can sometimes knock down the protein activity altogether. These molecules have been applied to studies in several model organisms, including mice, zebrafish, frogs and sea urchins.[1] Morpholinos can also modify the splicing of pre-mRNA[2] or inhibit the maturation and activity of miRNA.[3] Techniques for targeting Morpholinos to RNAs and delivering Morpholinos into cells have recently been reviewed in a journal article[4] and in book form.[5]

Morpholinos are in development as pharmaceutical therapeutics targeted against pathogenic organisms such as bacteria[6] or viruses[7] and genetic diseases.[8] A Morpholino-based drug eteplirsen from Sarepta Therapeutics received accelerated approval from the US Food and Drug Administration in September 2016 for the treatment of some mutations causing Duchenne muscular dystrophy,[9] although the approval process was mired in controversy. Other Morpholino-based drugs golodirsen, viltolarsen, and casimersen (also for Duchenne muscular dystrophy) were approved by the FDA in 2019–2021.[10][11][12]

  1. ^ Heasman J (March 2002). "Morpholino oligos: making sense of antisense?". Developmental Biology. 243 (2): 209–14. doi:10.1006/dbio.2001.0565. PMID 11884031.
  2. ^ Draper BW, Morcos PA, Kimmel CB (July 2001). "Inhibition of zebrafish fgf8 pre-mRNA splicing with morpholino oligos: a quantifiable method for gene knockdown". Genesis. 30 (3): 154–6. doi:10.1002/gene.1053. PMID 11477696.
  3. ^ Kloosterman WP, Lagendijk AK, Ketting RF, Moulton JD, Plasterk RH (August 2007). "Targeted inhibition of miRNA maturation with morpholinos reveals a role for miR-375 in pancreatic islet development". PLOS Biology. 5 (8): e203. doi:10.1371/journal.pbio.0050203. PMC 1925136. PMID 17676975. (This paper currently has an expression of concern, see doi:10.1371/journal.pbio.3001631, PMID 35486652. If this is an intentional citation to a such a paper, please replace {{expression of concern|...}} with {{expression of concern|...|intentional=yes}}.)
  4. ^ Moulton JD (2016). "Guide for Morpholino Users: Toward Therapeutics" (PDF). J Drug Discov Develop and Deliv. 3 (2): 1023.
  5. ^ Moulton HM, Moulton JD, eds. (2017). Morpholino Oligomers. Methods in Molecular Biology. Vol. 1565. Humana Press (Springer). p. 284. doi:10.1007/978-1-4939-6817-6. ISBN 978-1-4939-6815-2. S2CID 28338321.
  6. ^ Geller BL (April 2005). "Antibacterial antisense". Current Opinion in Molecular Therapeutics. 7 (2): 109–13. PMID 15844617.
  7. ^ Deas TS, Bennett CJ, Jones SA, Tilgner M, Ren P, Behr MJ, Stein DA, Iversen PL, Kramer LD, Bernard KA, Shi PY (July 2007). "In vitro resistance selection and in vivo efficacy of morpholino oligomers against West Nile virus". Antimicrobial Agents and Chemotherapy. 51 (7): 2470–82. doi:10.1128/AAC.00069-07. PMC 1913242. PMID 17485503.
  8. ^ McClorey G, Fall AM, Moulton HM, Iversen PL, Rasko JE, Ryan M, Fletcher S, Wilton SD (October 2006). "Induced dystrophin exon skipping in human muscle explants". Neuromuscular Disorders. 16 (9–10): 583–90. doi:10.1016/j.nmd.2006.05.017. PMID 16919955. S2CID 21338534.
  9. ^ "Press Announcements - FDA grants accelerated approval to first drug for Duchenne muscular dystrophy". Food and Drug Administration. 2019-09-10.
  10. ^ Commissioner, Office of the (2019-12-12). "FDA grants accelerated approval to first targeted treatment for rare Duchenne muscular dystrophy mutation". FDA. Retrieved 2019-12-14.
  11. ^ Roshmi, R. R.; Yokota, T. (October 2019). "Viltolarsen for the treatment of Duchenne muscular dystrophy". Drugs of Today. 55 (10): 627–639. doi:10.1358/dot.2019.55.10.3045038. ISSN 1699-3993. PMID 31720560. S2CID 207935659.
  12. ^ Shirley, Matt (May 2021). "Casimersen: First Approval". Drugs. 81 (7): 875–879. doi:10.1007/s40265-021-01512-2. ISSN 1179-1950. PMID 33861387. S2CID 233248050.