Delivering the Messenger: Advances in Technologies for Therapeutic mRNA Delivery

Abstract

mRNA has broad potential as a therapeutic. Current clinical efforts are focused on vaccination, protein replacement therapies, and treatment of genetic diseases. The clinical translation of mRNA therapeutics has been made possible through advances in the design of mRNA manufacturing and intracellular delivery methods. However, broad application of mRNA is still limited by the need for improved delivery systems. In this review, we discuss the challenges for clinical translation of mRNA-based therapeutics, with an emphasis on recent advances in biomaterials and delivery strategies, and we present an overview of the applications of mRNA-based delivery for protein therapy, gene editing, and vaccination. mRNA holds the potential to revolutionize vaccination, protein replacement therapies, and the treatment of genetic diseases. Since the first pre-clinical studies in the 1990s, 1 significant progress in the clinical translation of mRNA therapeutics has been made through advances in the design of mRNA manufacturing and intracellular delivery methods. 2 The translatability and stability of mRNA as well as its immunostimulatory activity are the key factors to be optimized for specific therapeutic application. 3 Increased translation and stability can be affected by many regions of the RNA. mRNA 5 0 and 3 0 UTRs are responsible for recruiting RNA-binding proteins and microRNAs, and they can profoundly affect translational activity. 2,4 The modification of rare codons in protein-coding sequences with synonymous frequently occurring codons, so-called codon optimization, can result in order-of-magnitude changes in expression levels. 5,6 Modification of the 5 0 mRNA cap can also enhance mRNA translation by inhibiting RNA decapping and improving resistance to enzymatic degradation. 7 Chemical modification of RNA bases can be used to modify mRNA immunostimulatory activity. 8,9 The importance of immunostimulation can depend on the application, 10 and, in some cases, it may actually improve performance, as in the case of vaccines. 11Finally, methods and vehicles for intracellular delivery remain the major barrier to the broad application of mRNA therapeutics. 12 With some exceptions, the intracellular delivery of mRNA is generally more challenging than that of small oligonucleotides, and it requires encapsulation into a delivery nanoparticle, in part due to the significantly larger size of mRNA molecules (300-5,000 kDa, 1-15 kb) as compared to other types of RNAs (small interfering RNAs [siRNAs], 14 kDa; antisense oligonucleotides [ASOs], 4-10 kDa). 10,13 In this review, we discuss the challenges for clinical translation of mRNAbased therapeutics, with an emphasis on recent advances in biomaterials and delivery strategies, and we present an overview of the applications of mRNA-based delivery for protein therapy, gene editing, and vaccination. Materials for mRNA Delivery Structural Aspects of Material DesignAmong the many barriers to function, mRNA must cross the cell membrane in order to reach the cytoplasm (Figure 1). The cell me...

Nanoparticles in the clinic: An update

“…It should be noted that other clinical trials investigating nanoparticles for the delivery of mRNA exist but since they are predominately delivered through intradermal or other routes of administration they will not be covered here. We point the reader to a recent review on mRNA delivery strategies where current clinical trials and delivery vehicles are a primary focus …”

“…We point the reader to a recent review on mRNA delivery strategies where current clinical trials and delivery vehicles are a primary focus. 19…”

Bundling mRNA Strands to Prepare Nano‐Assemblies with Enhanced Stability Towards RNase for In Vivo Delivery

“…Although the assembly of protein-coding RNAc an be also prepared by rolling circle transcription of plasmid DNA, aw idely-used method for the preparation of structured RNA, [11] protein transcription in this approach relies on an internal ribosomal entry site,w hich tends to yield am uch lower level of translational efficiencyc ompared to capdependent translation. [12] Our approach provides an additional mRNAstabilization mechanism different to that of previous approaches,including mRNAc omplexation with cationic polymers/lipids,a nd mRNAc hemical modification, and therefore,as ynergistic effect could be expected to result from the combinational use of R-NAs with these existing approaches.F urthermore,t he use of R-NAs alone without ac ationic carrier also yielded efficient protein production in vivo.W hile naked mRNAi s frequently used in clinical in vivo mRNAd elivery, [13] our system has the potential to improve efficiency of mRNA delivery in such settings.…”

The promise of mRNA vaccines: a biotech and industrial perspective

“…In addition to the aforementioned sustained stability imparted through protection from nuclease degradation, they also facilitate organ specificity, efficient cellular uptake, and provide endosomal escape properties that can enhance the successful delivery of the mRNA cargo to the cytoplasmic site of action. [34][35][36] There have been numerous examples of successful delivery of mRNA by using LNPs for therapeutic [37][38][39][40] as well as vaccine applications. [41][42][43][44] Much of the focus of the continued development of such LNP carrier systems involves optimization of the ionizable lipid component, with particular focus on the acid dissociation constant (pKa) and fusogenic properties (both of the ionizable component as well as helper lipid[s]), which have been demonstrated to play key roles in efficient cytoplasmic entry and release of cargo.…”