Chemical Manipulation of the Endosome Trafficking Machinery: Implications for Oligonucleotide Delivery

Abstract

Antisense oligonucleotides (ASOs), siRNA and splice switching oligonucleotides (SSOs) all have immense potential as therapeutic agents, potential that is now being validated as oligonucleotides enter the clinic. However, progress in oligonucleotide-based therapeutics has been limited by the difficulty in delivering these complex molecules to their sites of action in the cytosol or nucleus of cells within specific tissues. There are two aspects to the delivery problem. The first is that most types of oligonucleotides have poor uptake into non-hepatic tissues. The second is that much of the oligonucleotide that is taken up by cells is entrapped in endosomes where it is pharmacologically inert. It has become increasingly recognized that endosomal trapping is a key constraint on oligonucleotide therapeutics. Thus, many approaches have been devised to address this problem, primarily ones based on various nanoparticle technologies. However, recently an alternative approach has emerged that employs small molecules to manipulate intracellular trafficking processes so as to enhance oligonucleotide actions. This review presents the current status of this chemical biology approach to oligonucleotide delivery and seeks to point out possible paths for future development.

Endosomal escape of RNA therapeutics: How do we solve this rate-limiting problem?

“…Unfortunately, to date, the majority of effort has (likely) resulted in endosomal rupture with its inherent concomitant cytotoxicity due to release of a wide array of endosomally compartmentalized proteins and molecules into the cytoplasm resulting in activation of the innate immune system and other toxic pathways (Dowdy et al 2022). Rudy Juliano from the University of North Carolina has recently put forth a series of in-depth reviews describing these approaches and detailing the endocytotic routes of RNA therapeutics (Juliano et al 2018;Juliano 2018;Juliano 2021).…”

“…1). However, endosomes contain a lipid bilayer that entrap and retain ~99% of RNA therapeutics (Dowdy et al 2022;Juliano 2021). Indeed, using quantitative NanoSIMS microscopy, Haibo Jiang's lab at the University of Hong Kong determined that only 1-2% of GalNAc-ASO conjugates escape from endosomes in hepatocytes in vivo (He et al 2021).…”

“…Alternatively, fusion events between endosomes, multivesicular bodies and lysosomes potentially generate a temporary breach of the lipid bilayer for RNA therapeutics to leak into the cytoplasm (Dowdy et al 2022). Lastly, there is incomplete, but suggestive data, that RNA therapeutics may also escape via retro-transport from the Golgi (Juliano 2021). Due to the ~1% of RNA therapeutics that productively escapes from endosomes, definitively determining if any, or all, of these mechanisms are involved in endosomal escape has been technically challenging.…”

Potential Application of Small Interfering RNA in Gastro-Intestinal Tumors

“…As all NABDs [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ], siRNAs delivered systemically encounter several different biological barriers. In particular, they can: (1) be degraded by the nucleases present in the blood; (2) be removed by the phagocytic system, (3) be eliminated by the kidneys and/or sequestered in the liver [ 26 ] ( Figure 2 ).…”

Oligonucleotides-Based Therapeutics

“…Strategies to overcome the key issue of endosome entrapment after endocytosis has been described extensively by Juliano [11] with original proprietary tools.…”