Nucleic Acids Res. 2023 Apr 18. pii: gkad268. [Epub ahead of print]
Wei Liu,
Naoki Iwamoto,
Subramanian Marappan,
Khoa Luu,
Snehlata Tripathi,
Erin Purcell-Estabrook,
Juili Dilip Shelke,
Himali Shah,
Anthony Lamattina,
Qianli Pan,
Brett Schrand,
Frank Favaloro,
Mugdha Bedekar,
Arindom Chatterjee,
Jigar Desai,
Tomomi Kawamoto,
Genliang Lu,
Jake Metterville,
Milinda Samaraweera,
Priyanka Shiva Prakasha,
Hailin Yang,
Yuan Yin,
Hui Yu,
Paloma H Giangrande,
Michael Byrne,
Pachamuthu Kandasamy,
Chandra Vargeese.
Herein, we report the systematic investigation of stereopure phosphorothioate (PS) and phosphoryl guanidine (PN) linkages on siRNA-mediated silencing. The incorporation of appropriately positioned and configured stereopure PS and PN linkages to N-acetylgalactosamine (GalNAc)-conjugated siRNAs based on multiple targets (Ttr and HSD17B13) increased potency and durability of mRNA silencing in mouse hepatocytes in vivo compared with reference molecules based on clinically proven formats. The observation that the same modification pattern had beneficial effects on unrelated transcripts suggests that it may be generalizable. The effect of stereopure PN modification on silencing is modulated by 2'-ribose modifications in the vicinity, particularly on the nucleoside 3' to the linkage. These benefits corresponded with both an increase in thermal instability at the 5'-end of the antisense strand and improved Argonaute 2 (Ago2) loading. Application of one of our most effective designs to generate a GalNAc-siRNA targeting human HSD17B13 led to ∼80% silencing that persisted for at least 14 weeks after administration of a single 3 mg/kg subcutaneous dose in transgenic mice. The judicious use of stereopure PN linkages improved the silencing profile of GalNAc-siRNAs without disrupting endogenous RNA interference pathways and without elevating serum biomarkers for liver dysfunction, suggesting they may be suitable for therapeutic application.