Delivery of genetic molecules such as mRNA into cells is vital with important applications such as vaccine development. Various agents have been developed for mRNA delivery. However, conventional mRNA nanocarriers mainly focus on their physical interaction with mRNA molecules, or protection / delivery of mRNA, such as adjusting physical properties of nanocarriers to control binding with mRNA or cellular uptake.
Moreover, effective mRNA delivery in hard-to-transfect APCs remains a challenge. The hard-to-transfect nature in APCs is partly attributed to the suppressed mRNA translation associated with the intrinsic high intracellular glutathione (GSH) level.
Thus, tetrasulfide bond bridged DMONs modified with polyethylenimine (PEI) have been reported to oxidize GSH to GSSG (oxidized GSH) to upregulate mRNA translation in APCs. However, the intrinsic cellular regeneration of GSH from GSSG catalyzed by glutathione reductase (GR) could hinder the regulatory efficiency. Besides, the PEI modification to induce endosomal escape raises unwanted cytotoxicity.
Therefore, it is highly desired to develop a new mRNA delivery platform with good biocompatibility and long-term bioregulatory capability towards mRNA translation.
ZIF-8 is a type of metal organic frameworks and an emerging delivery system for a variety of molecules, including amino acids, proteins and plasmids. These biomolecules are generally encapsulated by biomimetic mineralization of ZIF-8, where ZIF-8 are mainly used as delivery vehicles.
To date, ZIF-8 has not been applied for mRNA delivery. Recent research indicates each components of ZIF-8 can possess great potential to regulate mRNA translation and enhance mRNA delivery: the acidic pH responsive breakage of zinc-ligand bonds in ZIF-8 is expected to release zinc for GR inhibition and GSSG reduction, and imidazole for endosomal escape.
In a new research article published in the Beijing-based National Science Review, the research team led by Professor Chengzhong Yu from the University of Queensland reports the confined growth of ZIF-8 nanocrystals partially in the large mesopores of DMONs (DMONs-ZIF-8) for long-term upregulated mRNA translation. Different from previous works, this delivery system avoids the use of cytotoxic polymer modification.
All components in DMONs-ZIF-8 contribute to mRNA delivery: (a) high mRNA loading capacity enabled by large mesopores for cellular uptake; (b) successful endosomal escape contributed by imidazole group in ZIF-8; and as a translation regulator for (c) synergistic GSH depletion by tetrasulfide-induced GSH oxidation and zinc-mediated inhibition of GR and GSSG reduction; (d-f) deactivated GAPDH involved mRNA translation inhibition and increased mitochondrial membrane potential (MMP) activated mTORC1 pathway; and consequently (g) enhanced mRNA translation.
DMONs-ZIF-8 exhibited higher mRNA translation modulation and delivery efficiency compared to polymer modified control (DMONs-PEI) and commercial products (in vitro: lipofectamine, in vivo: in vivo-jetPEI). This research provides new understandings in the rational design of functional nanocarriers for mRNA delivery towards APCs and paves the way to advance mRNA applications such as the development of mRNA vaccines.
This research received funding from the Australian Research Council (DP200102962).