Efficient mRNA delivery by branched lipids

mRNA molecules are large and chemically unstable, so a vector must be utilized to deliver mRNA to the cells. One of the most advanced technologies for the delivery of mRNA are (LNPs), which are composed of ionizable lipids, cholesterol, helper lipids and polyethylene glycol.

A team of researchers led by Assistant Professor Yusuke Sato and Professor Hideyoshi Harashima at the Faculty of Pharmaceutical Sciences, Hokkaido University, and by Kazuki Hashiba at the Nitto Denko Corporation have developed a novel branched ionizable lipid which, when included in LNPs, greatly increases the efficiency of mRNA delivery. Their results were published in the journal Small Science.

Previous work has shown that ionizable lipids with branching tails increases the efficiency of mRNA delivery by LNPs. However, two major issues have prevented a systematic analysis of the effect of branching ionizable lipids. First, tail branching leads to an enormous diversity of chemicals; second, the number of commercially available branching ionizable lipids is limited.

To overcome these hurdles, the researchers generated a systematic lipid library of branching ionizable lipids, and limited this library to a specific subset of branching lipids which could be described with just two parameters: total carbon number and symmetry. They then tested the 32 lipids in this library for their effect on the stability of LNPs containing mRNA (LNP-RNA).

Expression of EGFP (green) in the liver 24 hours after administering LNP-RNA containing EGFP mRNA. CL4F 8-6 was used to synthesize the LNP-RNA. Left, control; center, 0.5 mg/kg EGFP mRNA; right, 1.5 mg/kg EGFP mRNA. Blood vessels are in red. Credit: Kazuki Hashiba, Yusuke Sato, et al, Small Science, November 9, 2022

A cross-section of an LNP-RNA. The mRNA (red) is encapsulated by lipids (blue spheres with tails; Image: Yusuke Sato). Credit: Yusuke Sato

The structure of CL4F 8-6, the branched ionizable lipid that was most effective in increasing storage stability and LNP-RNA delivery (Image: Yusuke Sato). Credit: Yusuke Sato