Developments in siRNA Modification and Ligand Conjugated Delivery To Enhance RNA Interference Ability

Abstract

There is great potential for siRNA in treatment of diseases through the reduction of damaging protein translation by RNA interference. However, delivery and cell uptake of siRNA poses a serious problem in its therapeutic applications. Methods to overcome this issue include chemical modification of the siRNA duplex to improve pharmacokinetics, stability and efficacy and conjugation to small ligand molecules to enable membrane penetration, targetability and potency. In this review, the most common modifications of siRNA will be discussed, along with ligand conjugates that are believed to be the most promising in advancing the field of targeted siRNA delivery.

RNAi-Based Therapeutics and Novel RNA Bioengineering Technologies

“…First, structural optimization may improve RNAi potency and target selectivity besides improved metabolic stability ( Bramsen et al, 2009 ; Janas et al, 2018 ). Second, optimization may decrease therapeutic immunogenicity and therefore improve overall safety ( Robbins et al, 2007 ; Maguregui and Abe, 2020 ). Finally, optimization may increase tissue- or organ-targeting specificity by conjugating receptor specific ligands or by changing the physical conformation or chemical properties to increase uptake and endosomal escape into the cytosol ( Lönn et al, 2016 ; Shum and Rossi, 2016 ; Chakraborty et al, 2017 ; Foster et al, 2018 ; Janas et al, 2018 ; Maguregui and Abe, 2020 ; Zhang et al, 2021a ).…”

“…Once an RNAi drug is administered to the body, there are several physical and pharmacokinetic barriers that limit its actions and desired efficacy ( Fan and de Lannoy, 2014 ; Johannes and Lucchino, 2018 ; Seth et al, 2019 ; Smith et al, 2022 ). Chemical modifications and the development of novel delivery methods compatible with RNAi machinery help researchers overcome these barriers ( Maguregui and Abe, 2020 ; Smith et al, 2022 ). Although these modifications are intended to enhance stability and improve efficacy, growing evidence suggests that chemical modifications of in vivo synthesized RNAi molecules can increase the risk of off-target effects by altering their structure, folding, biologic activity, and safety away from natural RNAi agents ( Morena et al, 2018 ; Yu et al, 2019 ).…”

Azide‐Modified Nucleosides as Versatile Tools for Bioorthogonal Labeling and Functionalization

“…Site‐specific labelling and modification of nucleic acids in vitro and in cells is a prerequisite for studying all aspects of DNA and RNA function. In particular the discovery of the many different RNA types involved in the regulation of cellular processes, such as for example siRNAs, [1] ncRNAs, [2] or riboswitches [3–5] has put demand on synthetic chemistry to provide oligonucleotides (ONs) carrying specific labels or modifications. Catalytically active ONs (ribozymes) as integral part of the RNA world hypothesis have been synthesized in variants decorated with various modifications in the context of studies regarding the origin of life [6–8] …”

Photoregulation of Gene Expression with Ligand‐Modified Caged siRNAs through Host/Guest Interaction

“…Many chemical modification strategies have been developed to address these issues. Ligand‐modified siRNA is one of the important methods to enhance accumulation in specific tissues [5] . For example, cRGD‐conjugated siRNA can be receptor‐mediated endocytosis in α v β 3 positive cells to achieve luciferase gene silencing [6] .…”

“…Ligand-modified siRNA is one of the important methods to enhance accumulation in specific tissues. [5] For example, cRGD-conjugated siRNA can be receptor-mediated endocytosis in α v β 3 positive cells to achieve luciferase gene silencing. [6] N-acetygalactosamine (GalNAc) modified at the 3' terminus of sense strand siRNA can also enhance the target delivery to the liver through asialoglycoprotein receptor (ASGPR)-mediated endocytosis.…”