# Trivalent Disulfide Unit-Masked System Efficiently Delivers Large Oligonucleotide

## TL;DR

A new delivery system using a trivalent disulfide unit efficiently delivers large oligonucleotide drugs into cells without toxicity.

## Contribution

A novel trivalent disulfide unit-masked system for efficient and safe oligonucleotide delivery is developed.

## Key findings

- The system showed better cellular delivery efficiency than Lipo2000 without cytotoxicity.
- Thiol reagents reduced uptake, indicating endocytosis-independent delivery.
- In mice, the system rapidly distributed in liver tissues with over 24 h duration of action.

## Abstract

Oligonucleotide drugs are shining in clinical therapeutics, but efficient and safe delivery systems severely limit their widespread use. A disulfide unit technology platform based on dynamic thiol exchange chemistry at the cell membrane has the potential for drug delivery. However, the alteration of the disulfide unit CSSC dihedral angle induced by different substituents directly affects the effectiveness of this technology and its stability. Previously, we constructed a trivalent low dihedral angle disulfide unit that can effectively promote the cellular uptake of small molecules. Here, we constructed a novel disulfide unit-masked oligonucleotide hybrid based on a low dihedral angle disulfide unit, motivated by prodrug design. Cellular imaging results showed that such a system exhibited superior cellular delivery efficiency than the commercial Lipo2000 without cytotoxicity. The thiol reagents significantly reduced its cellular uptake (57–74%), which proved to be endocytosis-independent. In addition, in vivo distribution experiments in mice showed that such systems can be rapidly distributed in liver tissues with a duration of action of more than 24 h, representing a potential means of silencing genes involved in the pathogenesis of liver-like diseases. In conclusion, this trivalent disulfide unit-masked system we constructed can effectively deliver large oligonucleotide drugs.