Ribofuranose-based GalNAc-conjugated siRNA enhances the liver-targeted delivery and elicits robust RNAi-mediated gene silencing

The <i>N</i>-acetylgalactosamine (GalNAc)-conjugate delivery platform has emerged as a pivotal enabling technology for the clinical translation of oligonucleotide therapeutics. The development of GalNAc-conjugated small interfering RNA (siRNA) therapeutics has been significantly advanced through structural optimization of the delivery platform. Here, we report that a series of ribofuranose- and deoxyribofuranose-incorporated GalNAc-siRNA conjugates targeting proprotein convertase subtilisin/kexin type 9 (PCSK9) mRNA were synthesized and evaluated for their bioactivities and tissue distribution <i>in vivo</i>. When compared in detail with inclisiran, an approved siRNA drug that incorporates a triantennary GalNAc construct (designated L96) for targeted liver delivery, inc-G5, which contains ribofuranose ring within its GalNAc cluster, exhibits superior efficacy. Additionally, pharmacokinetic (PK) analysis in rats revealed that G5-conjugated siRNAs preferentially accumulate in the liver, have an extended elimination half-life, and exhibit the highest liver-to-kidney ratio, which indicated excellent liver delivery specificity. Moreover, the synthesis of G5 can be readily scaled up to the kilogram level, thereby providing robust support for the production of oligonucleotide drugs. These results underscore the critical application of ribofuranose integration in GalNAc-siRNA drugs, establishing G5 as a promising liver-targeted delivery moiety for siRNAs to achieve sustained gene silencing with improved hepatic specificity and therapeutic durability.