Fig. 5

Chemical modifications of splice switching oligonucleotides. a. Chemical modifications on phosphate backbone and ribose ring of SSOs. Unmodified RNA is shown for reference. PS, one of the phosphate backbone oxygen atom is replaced by a sulphur atom; 2′-MOE and 2′-OMe, PS-SSOs are often combined with ribose modifications including 2′-O-(2-methoxyethyl) or 2′O-methyl; PMO, charge-neutral nucleic acid, in which the six-membered morpholine ring replaces the five-membered ribose heterocycle; PPMO, positively charged peptides in PPMO dramatically improve intracellular uptake of PMO. VPMO, covalently linking MO to an octaguanidine dendrimer to improve delivery efficacy. LNA, the second and fourth of ribose form a rigid structure by shrinkage. PNA, a pseudo peptide polymer backbone substitutes for the phosphate backbone of RNA. b. Properties comparison of the common chemistries of antisense oligonucleotides