Impact of net charge, targeting ligand amount and mRNA modification on the uptake, intracellular routing and the transfection efficiency of mRNA lipopolyplexes in dendritic cells

Targeting mRNA formulations to achieve cell specificity is one of the challenges that must be tackled to mettle their therapeutic potential. Here, lipopolyplexes (LPR) bearing tri-mannose-lipid (TM) are used to target mannose receptor on dendritic cells. We investigated the impact of the net charge and percentage of TM units on the binding, uptake, transfection efficiency (TE) and RNA sensors activation. Binding and uptake capacities of naked and targeted LPR increase with the percent of cationic lipid, but the latter are 2-fold more up taken by the cells. Cationic LPR bearing 5 % and 10 % TM were localized in acidic compartments in contrast to naked LPR and 2.5 % TM-LPR. The drawback is the dramatic decrease of TE as the number of TM-units increases. Cationic LPR bearing 5 % and 10 % TM strongly induced NF-κB and PKR phosphorylation at 6 h. Conversely, mTOR is less activated in line with their low TE. Those side effects are overcome by using 5-methoxyuridine mRNA resulting in an improved TE due to non-phosphorylation of NF-κB and PKR and mTOR activation. Our results point out that targeting DC via mannose receptor triggers a higher uptake of cationic LPRs and fast routing to acidic compartments, and that efficient TE requires low number of TM units use or modified mRNA to escape RNA sensors activation to enhance the translation.

Intracellular Routing and Recognition of Lipid-Based mRNA Nanoparticles

Messenger RNA (mRNA) is being extensively used in gene therapy and vaccination due to its safety over DNA, in the following ways: its lack of integration risk, cytoplasmic expression, and transient expression compatible with fine regulations. However, clinical applications of mRNA are limited by its fast degradation by nucleases, and the activation of detrimental immune responses. Advances in mRNA applications, with the recent approval of COVID-19 vaccines, were fueled by optimization of the mRNA sequence and the development of mRNA delivery systems. Although delivery systems and mRNA sequence optimization have been abundantly reviewed, understanding of the intracellular processing of mRNA is mandatory to improve its applications. We will focus on lipid nanoparticles (LNPs) as they are the most advanced nanocarriers for the delivery of mRNA. Here, we will review how mRNA therapeutic potency can be affected by its interactions with cellular proteins and intracellular distribution.