The MOE Modification of RNA: Origins and Widescale Impact on the Oligonucleotide Therapeutics Field

Abstract

In an article published by Helvetica Chimica Acta in 1995, chemist P. Martin describes the synthesis of 2′‐O‐alkylated ribonucleosides for use in therapeutic antisense oligonucleotides (ASOs). This work was motivated by the need for a modified ribose structure that was compatible with solid‐phase synthesis protocols and that, when incorporated into an oligonucleotide, would render it resistant to nucleases without attenuating its ability to hybridize to a complementary RNA target. Martin described a robust route to 2′‐O‐alkylribonucleosides in which the ribose 2′‐OH group is substituted with 2′‐ethylene glycol derivatives. Oligonucleotides containing these modifications displayed überraschende Eigenschaften – ‘surprising properties’ – notably, higher affinity and specificity for RNA substrates and greater stability to nucleases relative to their unmodified counterparts. Today, the 2′‐ethylene glycol modification is universally known in the field as the 2′‐O‐methoxyethyl (MOE) modification. The chemistry features in four ASO drugs and many others in clinical trials. Here, we 1) summarize the synthesis of the MOE‐modified ribose; 2) outline the properties of MOE‐modified oligonucleotides as reported in Martin’s article; 3) highlight the first approved MOE‐modified ASO drugs, mipomersen and nusinersen; and 4) survey MOE‐modified ASOs in clinical development. In the outlook, we put these developments into context and consider future possibilities for the MOE modification.

Peptide Conjugates of a 2′-O-Methoxyethyl Phosphorothioate Splice-Switching Oligonucleotide Show Increased Entrapment in Endosomes

“…For oligonucleotides with MOE ribose chemistry, the same mismatch at an MOE:RNA base pair reduced the T m by 8.8 °C (Figure C). This value falls within the expected range for MOE:RNA mismatches (i.e., Δ T m of −3.6 to −9.2 °C per mismatch) . Of note, the c.315-48C-targeting MOE PS ON5 displayed a higher T m than the c.315-48C-targeting DNA/LNA PS ON2 (Figure C).…”

“…Interestingly, the PS modification also promotes the free uptake of ASOs into cells in a process termed gymnosis. , Gymnotic delivery is attributed to the interaction of PS ASOs with heparin-binding proteins on the cell surface but remains an incompletely understood phenomenon, with dependence on oligonucleotide sequence, length, , chemistry, , and concentration ,, as well as cell type , and physiological state . Second-generation (e.g., 2′- O -methoxyethyl, or MOE, and locked nucleic acid, or LNA , ) modifications further increase the nuclease stability of PS ASOs and offset losses in RNA target-binding affinity caused by the PS groups (Δ T m of −0.5 °C per substitution) . Presently, ASOs of the MOE chemical class have been evaluated in thousands of humans, and five MOE PS ASOs are approved drugs …”

Future directions for medicinal chemistry in the field of oligonucleotide therapeutics

“…The MOE modification is today the most widely used chemical modification of single-stranded oligonucleotide drugs (reviewed in [20] ). The modification was clinically validated with the approval of mipomersen, a 20-mer "gapmer" PS oligonucleotide bearing five MOE-modified riboses flanking a 10-mer DNA "window".…”

GGC expansion inZFHX3causes SCA4 and impairs autophagy

“…Intriguingly, they also suggest crosstalk between the polyQ protein ATXN2 and ZFHX3 polyG pathology. Reduction of ATXN2 by treatment with ASOs with the MOE gapmer chemistry 28 improved neurodegeneration in mouse models of SCA2 and ALS 29,30 ; an ASO to ATXN2 is currently in a phase 1 trial for sporadic ALS (NCT04494256). Future studies will need to address whether reduction of wildtype ATXN2 can reduce ZFHX3-polyG toxicity.…”