Screening of mRNA Chemical Modification to Maximize Protein Expression with Reduced Immunogenicity

An mRNA-encoded dominant-negative inhibitor of transcription factor RUNX1 suppresses vitreoretinal disease in experimental models

Messenger RNA (mRNA)-based therapies are a promising approach to medical treatment. Except for infectious diseases, no other disease has mRNA-based therapies available. The eye is an ideal model for mRNA therapeutic development because it requires limited dosing. Proliferative vitreoretinopathy (PVR) is a blinding condition caused by retinal detachment that now lacks available medical treatment, with surgery as the only treatment option. We previously implicated runt-related transcription factor-1 (RUNX1) as a driver of epithelial-to-mesenchymal transition (EMT) in PVR and as a critical mediator of aberrant ocular angiogenesis when up-regulated. On the basis of these findings, an mRNA was designed to express a dominant-negative inhibitor of RUNX1 (RUNX1-Trap). We show that RUNX1-Trap delivered in polymer-lipidoid complexes or lipid nanoparticles sequestered RUNX1 in the cytosol and strongly reduced proliferation in primary cell cultures established from fibrotic membranes derived from patients with PVR. We assessed the preclinical efficacy of intraocular delivery of mRNA-encoded RUNX1-Trap in a rabbit model of PVR and in a laser-induced mouse model of aberrant angiogenesis often used to study wet age-related macular degeneration. mRNA-encoded RUNX1-Trap suppressed ocular pathology, measured as pathological scores in the rabbit PVR model and leakage and lesion size in the laser-induced choroidal neovascularization mouse model. mRNA-encoded RUNX1-Trap also strongly reduced proliferation in a human ex vivo explant model of PVR. These data demonstrate the therapeutic potential of mRNA-encoded therapeutic molecules with dominant-negative properties, highlighting the potential of mRNA-based therapies beyond standard gene supplementation approaches.

mRNA-based therapeutic strategies for cancer treatment

In the rapidly evolving landscape of medical research, the emergence of RNA-based therapeutics is paradigm shifting. It is mainly driven by the molecular adaptability and capacity to provide precision in targeting. The coronavirus disease 2019 pandemic crisis underscored the effectiveness of the mRNA therapeutic development platform and brought it to the forefront of RNA-based interventions. These RNA-based therapeutic approaches can reshape gene expression, manipulate cellular functions, and correct the aberrant molecular processes underlying various diseases. The new technologies hold the potential to engineer and deliver tailored therapeutic agents to tackle genetic disorders, cancers, and infectious diseases in a highly personalized and precisely tuned manner. The review discusses the most recent advancements in the field of mRNA therapeutics for cancer treatment, with a focus on the features of the most utilized RNA-based therapeutic interventions, current pre-clinical and clinical developments, and the remaining challenges in delivery strategies, effectiveness, and safety considerations.

Self-feedback loop-containing synthetic mRNA switches for controlled microRNA sensing

Synthetic mRNA switches are powerful cell fate manipulation tools that sense cellular input molecules to directly control protein expression at the translational level. The lack of available switch designs that can mimic the natural sophisticated protein regulation is a fundamental issue that limits the application of synthetic mRNA switches. Here we report a new set of synthetic mRNA switches by incorporating self-feedback loop machineries to dynamically control protein expression levels upon sensing cellular microRNAs. We redesigned the coding region of the switch to express output protein along with mRNA regulatory proteins. RNA-binding proteins (RBPs) and RBP-binding RNA motifs (aptamers) guide the regulatory proteins to act on their own mRNAs, enhancing or flattening the effect of microRNA sensing. Importantly, we demonstrated that the switches with the positive feedback feature can enlarge a high-or-low microRNA effect into a nearly all-or-none pattern, substantially boosting the use of synthetic mRNA switches as high-performance microRNA sensors or binary cell regulation tools. We believe these novel mRNA switch designs provide new strategies to construct complex mRNA-based genetic circuits for future molecular sensing and cell engineering.

Messenger RNA Therapy for Female Reproductive Health

Female reproductive health has traditionally been an underrepresented area of research in the drug delivery sciences. This disparity is also seen in the emerging field of mRNA therapeutics, a class of medicines that promises to treat and prevent disease by upregulating protein expression in the body. Here, we review advances in mRNA therapies through the lens of improving female reproductive health. Specifically, we begin our review by discussing the fundamental structure and biochemical modifications associated with mRNA-based drugs. Then, we discuss various packaging technologies, including lipid nanoparticles, that can be utilized to protect and transport mRNA drugs to target cells in the body. Last, we conclude our review by discussing the usage of mRNA therapy for addressing pregnancy-related health and vaccination against sexually transmitted diseases in women. Of note, we also highlight relevant clinical trials using mRNA for female reproductive health while also providing their corresponding National Clinical Trial identifiers. In undertaking this review, our aim is to provide a fundamental background understanding of mRNA therapy and its usage to specifically address female health issues with an overarching goal of providing information toward addressing gender disparity in certain aspects of health research.

Neoantigen vaccine nanoformulations based on Chemically synthesized minimal mRNA (CmRNA): small molecules, big impact

Recently, chemically synthesized minimal mRNA (CmRNA) has emerged as a promising alternative to in vitro transcribed mRNA (IVT-mRNA) for cancer therapy and immunotherapy. CmRNA lacking the untranslated regions and polyadenylation exhibits enhanced stability and efficiency. Encapsulation of CmRNA within lipid-polymer hybrid nanoparticles (LPPs) offers an effective approach for personalized neoantigen mRNA vaccines with improved control over tumor growth. LPP-based delivery systems provide superior pharmacokinetics, stability, and lower toxicity compared to viral vectors, naked mRNA, or lipid nanoparticles that are commonly used for mRNA delivery. Precise customization of LPPs in terms of size, surface charge, and composition allows for optimized cellular uptake, target specificity, and immune stimulation. CmRNA-encoded neo-antigens demonstrate high translational efficiency, enabling immune recognition by CD8+ T cells upon processing and presentation. This perspective highlights the potential benefits, challenges, and future directions of CmRNA neoantigen vaccines in cancer therapy compared to Circular RNAs and IVT-mRNA. Further research is needed to optimize vaccine design, delivery, and safety assessment in clinical trials. Nevertheless, personalized LPP-CmRNA vaccines hold great potential for advancing cancer immunotherapy, paving the way for personalized medicine.

Cell Reprogramming and Differentiation Utilizing Messenger RNA for Regenerative Medicine

The COVID-19 pandemic generated interest in the medicinal applications of messenger RNA (mRNA). It is expected that mRNA will be applied, not only to vaccines, but also to regenerative medicine. The purity of mRNA is important for its medicinal applications. However, the current mRNA synthesis techniques exhibit problems, including the contamination of undesired 5'-uncapped mRNA and double-stranded RNA. Recently, our group developed a completely capped mRNA synthesis technology that contributes to the progress of mRNA research. The introduction of chemically modified nucleosides, such as N1-methylpseudouridine and 5-methylcytidine, has been reported by Karikó and Weissman, opening a path for the practical application of mRNA for vaccines and regenerative medicine. Yamanaka reported the production of induced pluripotent stem cells (iPSCs) by introducing four types of genes using a retrovirus vector. iPSCs are widely used for research on regenerative medicine and the preparation of disease models to screen new drug candidates. Among the Yamanaka factors, Klf4 and c-Myc are oncogenes, and there is a risk of tumor development if these are integrated into genomic DNA. Therefore, regenerative medicine using mRNA, which poses no risk of genome insertion, has attracted attention. In this review, the author summarizes techniques for synthesizing mRNA and its application in regenerative medicine.

The mRNA Vaccine Revolution: COVID-19 Has Launched the Future of Vaccinology

During the COVID-19 pandemic, mRNA (mRNA) vaccines emerged as leading vaccine candidates in a record time. Nonreplicating mRNA (NRM) and self-amplifying mRNA (SAM) technologies have been developed into high-performing and clinically viable vaccines against a range of infectious agents, notably SARS-CoV-2. mRNA vaccines demonstrate efficient in vivo delivery, long-lasting stability, and nonexistent risk of infection. The stability and translational efficiency of in vitro transcription (IVT)-mRNA can be further increased by modulating its structural elements. In this review, we present a comprehensive overview of the recent advances, key applications, and future challenges in the field of mRNA-based vaccinology.

A precise and efficient circular RNA synthesis system based on a ribozyme derived from Tetrahymena thermophila

Classic strategies for circular RNA (circRNA) preparation always introduce large numbers of linear transcripts or extra nucleotides to the circularized product. In this study, we aimed to develop an efficient system for circRNA preparation based on a self-splicing ribozyme derived from an optimized Tetrahymena thermophila group Ⅰ intron. The target RNA sequence was inserted downstream of the ribozyme and a complementary antisense region was added upstream of the ribozyme to assist cyclization. Then, we compared the circularization efficiency of ribozyme or flanking intronic complementary sequence (ICS)-mediated methods through the DNMT1, CDR1as, FOXO3, and HIPK3 genes and found that the efficiency of our system was remarkably higher than that of flanking ICS-mediated method. Consequently, the circularized products mediated by ribozyme are not introduced with additional nucleotides. Meanwhile, the overexpressed circFOXO3 maintained its biological functions in regulating cell proliferation, migration, and apoptosis. Finally, a ribozyme-based circular mRNA expression system was demonstrated with a split green fluorescent protein (GFP) using an optimized Coxsackievirus B3 (CVB3) internal ribosome entry site (IRES) sequence, and this system achieved successful translation of circularized mRNA. Therefore, this novel, convenient, and rapid engineering RNA circularization system can be applied for the functional study and large-scale preparation of circular RNA in the future.

Polyplex designs for improving the stability and safety of RNA therapeutics

Nanoparticle-based delivery systems have contributed to the recent clinical success of RNA therapeutics, including siRNA and mRNA. RNA delivery using polymers has several distinct properties, such as enabling RNA delivery into extra-hepatic organs, modulation of immune responses to RNA, and regulation of intracellular RNA release. However, delivery systems should overcome safety and stability issues to achieve widespread therapeutic applications. Safety concerns include direct damage to cellular components, innate and adaptive immune responses, complement activation, and interaction with surrounding molecules and cells in the blood circulation. The stability of the delivery systems should balance extracellular RNA protection and controlled intracellular RNA release, which requires optimization for each RNA species. Further, polymer designs for improving safety and stability often conflict with each other. This review covers advances in polymer-based approaches to address these issues over several years, focusing on biological understanding and design concepts for delivery systems rather than material chemistry.

Comb-structured mRNA vaccine tethered with short double-stranded RNA adjuvants maximizes cellular immunity for cancer treatment

Integrating antigen-encoding mRNA (Messenger RNA) and immunostimulatory adjuvant into a single formulation is a promising approach to potentiating the efficacy of mRNA vaccines. Here, we developed a scheme based on RNA engineering to integrate adjuvancy directly into antigen-encoding mRNA strands without hampering the ability to express antigen proteins. Short double-stranded RNA (dsRNA) was designed to target retinoic acid-inducible gene-I (RIG-I), an innate immune receptor, for effective cancer vaccination and then tethered onto the mRNA strand via hybridization. Tuning the dsRNA structure and microenvironment by changing its length and sequence enabled the determination of the structure of dsRNA-tethered mRNA efficiently stimulating RIG-I. Eventually, the formulation loaded with dsRNA-tethered mRNA of the optimal structure effectively activated mouse and human dendritic cells and drove them to secrete a broad spectrum of proinflammatory cytokines without increasing the secretion of anti-inflammatory cytokines. Notably, the immunostimulating intensity was tunable by modulating the number of dsRNA along the mRNA strand, which prevents excessive immunostimulation. Versatility in the applicable formulation is a practical advantage of the dsRNA-tethered mRNA. Its formulation with three existing systems, i.e., anionic lipoplex, ionizable lipid-based lipid nanoparticles, and polyplex micelles, induced appreciable cellular immunity in the mice model. Of particular interest, dsRNA-tethered mRNA encoding ovalbumin (OVA) formulated in anionic lipoplex used in clinical trials exerted a significant therapeutic effect in the mouse lymphoma (E.G7-OVA) model. In conclusion, the system developed here provides a simple and robust platform to supply the desired intensity of immunostimulation in various formulations of mRNA cancer vaccines.

Modified mRNA as a Treatment for Myocardial Infarction

Myocardial infarction (MI) is a severe disease with high mortality worldwide. However, regenerative approaches remain limited and with poor efficacy. The major difficulty during MI is the substantial loss of cardiomyocytes (CMs) with limited capacity to regenerate. As a result, for decades, researchers have been engaged in developing useful therapies for myocardial regeneration. Gene therapy is an emerging approach for promoting myocardial regeneration. Modified mRNA (modRNA) is a highly potential delivery vector for gene transfer with its properties of efficiency, non-immunogenicity, transiency, and relative safety. Here, we discuss the optimization of modRNA-based therapy, including gene modification and delivery vectors of modRNA. Moreover, the effective of modRNA in animal MI treatment is also discussed. We conclude that modRNA-based therapy with appropriate therapeutical genes can potentially treat MI by directly promoting proliferation and differentiation, inhibiting apoptosis of CMs, as well as enhancing paracrine effects in terms of promoting angiogenesis and inhibiting fibrosis in heart milieu. Finally, we summarize the current challenges of modRNA-based cardiac treatment and look forward to the future direction of such treatment for MI. Further advanced clinical trials incorporating more MI patients should be conducted in order for modRNA therapy to become practical and feasible in real-world treatment.

Cytidine-containing tails robustly enhance and prolong protein production of synthetic mRNA in cell and in vivo

Synthetic mRNAs are rising rapidly as alternative therapeutic agents for delivery of proteins. However, the practical use of synthetic mRNAs has been restricted by their low cellular stability as well as poor protein production efficiency. The key roles of poly(A) tail on mRNA biology inspire us to explore the optimization of tail sequence to overcome the aforementioned limitations. Here, the systematic substitution of non-A nucleotides in the tails revealed that cytidine-containing tails can substantially enhance the protein production rate and duration of synthetic mRNAs both in vitro and in vivo. Such C-containing tails shield synthetic mRNAs from deadenylase CCR4-NOT transcription complex, as the catalytic CNOT proteins, especially CNOT6L and CNOT7, have lower efficiency in trimming of cytidine. Consistently, these enhancement effects of C-containing tails were observed on all synthetic mRNAs tested and were independent of transfection reagents and cell types. As the C-containing tails can be used along with other mRNA enhancement technologies to synergically boost protein production, we believe that these tails can be broadly used on synthetic mRNAs to directly promote their clinical applications.

A Biostable l-DNA Hydrogel with Improved Stability for Biomedical Applications

DNA hydrogels have attracted increasing attention owing to their excellent permeability and high mechanical strength, together with thixotropy, versatile programmability and good biocompatibility. However, the moderate biostability and immune stimulation of DNA have arisen as big concerns for future potential clinical applications. Herein, we report the self-assembly of a novel l-DNA hydrogel, which inherited the extraordinary physical properties of a d-DNA hydrogel. With the mirror-isomer deoxyribose, this hydrogel exhibited improved biostability, withstanding fetal bovine serum (FBS) for at least 1 month without evident decay of its mechanical properties. The low inflammatory response of the l-DNA hydrogel has been verified both in vitro and in vivo. Hence, this l-DNA hydrogel with outstanding biostability and biocompatibility can be anticipated to serve as an ideal 3D cell-culture matrix and implanted bio-scaffold for long-term biomedical applications.

The Pivotal Role of Chemical Modifications in mRNA Therapeutics

After over a decade of development, mRNA has recently matured into a potent modality for therapeutics. The advantages of mRNA therapeutics, including their rapid development and scalability, have been highlighted due to the SARS-CoV-2 pandemic, in which the first two clinically approved mRNA vaccines have been spotlighted. These vaccines, as well as multiple other mRNA therapeutic candidates, are modified to modulate their immunogenicity, stability, and translational efficiency. Despite the importance of mRNA modifications for harnessing the full efficacy of mRNA drugs, the full breadth of potential modifications has yet to be explored clinically. In this review, we survey the field of mRNA modifications, highlighting their ability to tune the properties of mRNAs. These include cap and tail modifications, nucleoside substitutions, and chimeric mRNAs, each of which represents a component of mRNA that can be exploited for modification. Additionally, we cover clinical and preclinical trials of the modified mRNA platform not only to illustrate the promise of modified mRNAs but also to call attention to the room for diversifying future therapeutics.

Complete Chemical Synthesis of Minimal Messenger RNA by Efficient Chemical Capping Reaction

Site-specific chemical modification of mRNA can improve its translational efficiency and stability. For this purpose, it is desirable to develop a complete chemical synthesis method for chemically modified mRNA. The key is a chemical reaction that introduces a cap structure into the chemically synthesized RNA. In this study, we developed a fast and quantitative chemical capping reaction between 5'-phosphorylated RNA and N⁷-methylated GDP imidazolide in the presence of 1-methylimidazole in the organic solvent dimethyl sulfoxide. It enabled quantitative preparation of capping RNA within 3 h. We prepared chemically modified 107-nucleotide mRNAs, including N⁶-methyladenosine, insertion of non-nucleotide linkers, and 2'-O-methylated nucleotides at the 5' end and evaluated their effects on translational activity in cultured HeLa cells. The results showed that mRNAs with non-nucleotide linkers in the untranslated regions were sufficiently tolerant to translation and that mRNAs with the Cap_2 structure had higher translational activity than those with the Cap_0 structure.

Optogenetic reporters delivered as mRNA facilitate repeatable action potential and calcium handling assessment in human iPSC-derived cardiomyocytes

Electrical activity and intracellular Ca 2+ transients are key features of cardiomyocytes. They can be measured using organic voltage- and Ca 2+-sensitive dyes but their photostability and phototoxicity means they are unsuitable for long-term measurements. Here, we investigated whether genetically-encoded voltage and Ca 2+ indicators (GEVIs and GECIs) delivered as modified mRNA (modRNA) into human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) would be accurate alternatives allowing measurements over long periods. These indicators were detected in hiPSC-CMs for up to 7 days after transfection and did not affect responses to proarrhythmic compounds. Furthermore, using the GEVI ASAP2f we observed action potential prolongation in long QT syndrome models, while the GECI jRCaMP1b facilitated the repeated evaluation of Ca 2+ handling responses for various tyrosine kinase inhibitors. This study demonstrated that modRNAs encoding optogenetic constructs report cardiac physiology in hiPSC-CMs without toxicity or the need for stable integration, illustrating their value as alternatives to organic dyes or other gene delivery methods for expressing transgenes.

RNA-Based Strategies for Cell Reprogramming toward Pluripotency

Cell therapy approaches to treat a wide range of pathologies have greatly benefited from cell reprogramming techniques that allow the conversion of a somatic cell into a pluripotent cell. Many technological developments have been made since the initial major discovery of this biological process. Recently reprogramming methods based on the use of RNA have emerged and seem very promising. Thus, in this review we will focus on presenting the interest of such methods for cell reprogramming but also how these RNA-based strategies can be extended to eventually lead to medical applications to improve healthspan and longevity.

mRNA-Based Vaccines and Mode of Action

In the past 20 years, the mRNA vaccine technology has evolved from the first proof of concept to the first licensed vaccine against emerging pandemics such as SARS-CoV-2. Two mRNA vaccines targeting SARS-CoV-2 have received emergency use authorization by US FDA, conditional marketing authorization by EMA, as well as multiple additional national regulatory authorities. The simple composition of an mRNA encoding the antigen formulated in a lipid nanoparticle enables a fast adaptation to new emerging pathogens. This can speed up vaccine development in pandemics from antigen and sequence selection to clinical trial to only a few months. mRNA vaccines are well tolerated and efficacious in animal models for multiple pathogens and will further contribute to the development of vaccines for other unaddressed diseases. Here, we give an overview of the mRNA vaccine design and factors for further optimization of this new promising technology and discuss current knowledge on the mode of action of mRNA vaccines interacting with the innate and adaptive immune system.

Protein-Based Systems for Translational Regulation of Synthetic mRNAs in Mammalian Cells

Synthetic mRNAs, which are produced by in vitro transcription, have been recently attracting attention because they can express any transgenes without the risk of insertional mutagenesis. Although current synthetic mRNA medicine is not designed for spatiotemporal or cell-selective regulation, many preclinical studies have developed the systems for the translational regulation of synthetic mRNAs. Such translational regulation systems will cope with high efficacy and low adverse effects by producing the appropriate amount of therapeutic proteins, depending on the context. Protein-based regulation is one of the most promising approaches for the translational regulation of synthetic mRNAs. As synthetic mRNAs can encode not only output proteins but also regulator proteins, all components of protein-based regulation systems can be delivered as synthetic mRNAs. In addition, in the protein-based regulation systems, the output protein can be utilized as the input for the subsequent regulation to construct multi-layered gene circuits, which enable complex and sophisticated regulation. In this review, I introduce what types of proteins have been used for translational regulation, how to combine them, and how to design effective gene circuits.

PEGylation of mRNA by Hybridization of Complementary PEG-RNA Oligonucleotides Stabilizes mRNA without Using Cationic Materials

Messenger RNA (mRNA) delivery strategies are required to protect biologically fragile mRNA from ribonuclease (RNase) attacks to achieve efficient therapeutic protein expression. To tackle this issue, most mRNA delivery systems have used cationic components, which form electrostatically driven complexes with mRNA and shield encapsulated mRNA strands. However, cationic materials interact with anionic biomacromolecules in physiological environments, which leads to unspecific reactions and toxicities. To circumvent this issue of cation-based approaches, herein, we propose a cation-free delivery strategy by hybridization of PEGylated RNA oligonucleotides with mRNA. The PEG strands on the mRNA sterically and electrostatically shielded the mRNA, improving mRNA nuclease stability 15-fold after serum incubation compared with unhybridized mRNA. Eventually, the PEGylated mRNA induced nearly 20-fold higher efficiency of reporter protein expression than unhybridized mRNA in cultured cells. This study provides a platform to establish a safe and efficient cation-free mRNA delivery system.

Multifunctional Immunoadjuvants for Use in Minimalist Nucleic Acid Vaccines

Subunit vaccines based on antigen-encoding nucleic acids have shown great promise for antigen-specific immunization against cancer and infectious diseases. Vaccines require immunostimulatory adjuvants to activate the innate immune system and trigger specific adaptive immune responses. However, the incorporation of immunoadjuvants into nonviral nucleic acid delivery systems often results in fairly complex structures that are difficult to mass-produce and characterize. In recent years, minimalist approaches have emerged to reduce the number of components used in vaccines. In these approaches, delivery materials, such as lipids and polymers, and/or pDNA/mRNA are designed to simultaneously possess several functionalities of immunostimulatory adjuvants. Such multifunctional immunoadjuvants encode antigens, encapsulate nucleic acids, and control their pharmacokinetic or cellular fate. Herein, we review a diverse class of multifunctional immunoadjuvants in nucleic acid subunit vaccines and provide a detailed description of their mechanisms of adjuvanticity and induction of specific immune responses.

In Vivo bone tissue induction by freeze-dried collagen-nanohydroxyapatite matrix loaded with BMP2/NS1 mRNAs lipopolyplexes

Messenger RNA (mRNA) activated matrices (RAMs) are interesting to orchestrate tissue and organ regeneration due to the in-situ and sustained production of functional proteins. However, the immunogenicity of in vitro transcribed mRNA and the paucity of proper in vivo mRNA delivery vector need to be overcome to exert the therapeutic potential of RAM. We developed a dual mRNAs system for in vitro osteogenesis by co-delivering NS1 mRNA with BMP2 mRNA to inhibit RNA sensors and enhance BMP-2 expression. Next, we evaluated a lipopolyplex (LPR) formulation platform for in vivo mRNA delivery and adapted the LPRs for RAM preparation. The LPR formulated BMP2/NS1 mRNAs were incorporated into an optimized collagen-nanohydroxyapatite scaffold and freeze-dried to prepare ready-to-use RAMs. The loaded BMP2/NS1 mRNAs lipopolyplexes maintained their spherical morphology in the RAM, thanks to the core-shell structure of LPR. The mRNAs release from RAMs lasted for 16 days resulting in an enhanced prolonged transgene expression period compared to direct cell transfection. Once subcutaneously implanted in mice, the BMP2/NS1 mRNAs LPRs containing RAMs (RAM-BMP2/NS1) induced significant new bone tissue than those without NS1 mRNA, eight weeks post implantation. Overall, our results demonstrate that the BMP2/NS1 dual mRNAs system is suitable for osteogenic engagement, and the freeze-dried RAM-BMP2/NS1 could be promising off-the-shelf products for clinical orthopedic practice.

Exquisitely Specific anti-KRAS Biodegraders Inform on the Cellular Prevalence of Nucleotide-Loaded States

Mutations to RAS proteins (H-, N-, and K-RAS) are among the most common oncogenic drivers, and tumors harboring these lesions are some of the most difficult to treat. Although covalent small molecules against KRAS^G12C have shown promising efficacy against lung cancers, traditional barriers remain for drugging the more prevalent KRAS^G12D and KRAS^G12V mutants. Targeted degradation has emerged as an attractive alternative approach, but for KRAS, identification of the required high-affinity ligands continues to be a challenge. Another significant hurdle is the discovery of a hybrid molecule that appends an E3 ligase-recruiting moiety in a manner that satisfies the precise geometries required for productive polyubiquitin transfer while maintaining favorable druglike properties. To gain insights into the advantages and feasibility of KRAS targeted degradation, we applied a protein-based degrader (biodegrader) approach. This workflow centers on the intracellular expression of a chimeric protein consisting of a high-affinity target-binding domain fused to an engineered E3 ligase adapter. A series of anti-RAS biodegraders spanning different RAS isoform/nucleotide-state specificities and leveraging different E3 ligases provided definitive evidence for RAS degradability. Further, these established that the functional consequences of KRAS degradation are context dependent. Of broader significance, using the exquisite degradation specificity that biodegraders can possess, we demonstrated how this technology can be applied to answer questions that other approaches cannot. Specifically, application of the GDP-state specific degrader uncovered the relative prevalence of the "off-state" of WT and various KRAS mutants in the cellular context. Finally, if delivery challenges can be addressed, anti-RAS biodegraders will be exciting candidates for clinical development.

Anionic Complex with Efficient Expression and Good Safety Profile for mRNA Delivery

We previously found that a complex comprising plasmid DNA (pDNA), polyethylenimine (PEI), and γ-polyglutamic acid (γ-PGA) had high transgene efficiency without cytotoxicity in vitro and in vivo. However, messenger RNA (mRNA) remains an attractive alternative to pDNA. In this study, we developed a safe and effective delivery system for mRNA to prevent its degradation and efficiently deliver it into target cells. Various cationic and anionic complexes were produced containing PEI, γ-PGA, and an mRNA encoding firefly luciferase. Their physicochemical properties and cytotoxicities were analyzed and the in vitro and in vivo protein expression were determined. The cationic mRNA/PEI complex showed high in vitro protein expression with strong cytotoxicity. The anionic complex was constructed as mRNA/PEI8/γ-PGA12 complex with a theoretical charge ratio of 1:8:12 based on the phosphate groups of the mRNA, nitrogen groups of PEI, and carboxylate groups of γ-PGA. It was stable and showed high in vitro protein expression without cytotoxicity. After intravenous administration of mRNA/PEI8/γ-PGA12 complex to mice, high protein expression was observed in the spleen and liver and slight expression was observed in the lung over 24 h. Thus, the newly constructed mRNA/PEI8/γ-PGA12 complex provides a safe and effective strategy for the delivery of mRNA.

Polymeric delivery systems for nucleic acid therapeutics: Approaching the clinic

Gene therapy using nucleic acids has many clinical applications for the treatment of diseases with a genetic origin as well as for the development of innovative vaccine formulations. Since nucleic acids in their free form are rapidly degraded by nucleases present in extracellular matrices, have poor pharmacokinetics and hardly pass cellular membranes, carrier systems are required. Suitable carriers that protect the nucleic acid payload against enzymatic attack, prolong circulation time after systemic administration and assist in cellular binding and internalization are needed to develop nucleic acid based drug products. Viral vectors have been investigated and are also clinically used as delivery vehicles. However, some major drawbacks are associated with their use. Therefore there has been substantial attention on the use of non-viral carrier systems based on cationic lipids and polymers. This review focuses on the properties of polymer-based nucleic acid formulations, also referred as polyplexes. Different polymeric systems are summarized, and the cellular barriers polyplexes encounter and ways to tackle these are discussed. Finally attention is given to the clinical status of non-viral nucleic acid formulations.

Reverse C-glycosidase reaction provides C-nucleotide building blocks of xenobiotic nucleic acids

C-Analogues of the canonical N-nucleosides have considerable importance in medicinal chemistry and are promising building blocks of xenobiotic nucleic acids (XNA) in synthetic biology. Although well established for synthesis of N-nucleosides, biocatalytic methods are lacking in C-nucleoside synthetic chemistry. Here, we identify pseudouridine monophosphate C-glycosidase for selective 5-β-C-glycosylation of uracil and derivatives thereof from pentose 5-phosphate (D-ribose, 2-deoxy-D-ribose, D-arabinose, D-xylose) substrates. Substrate requirements of the enzymatic reaction are consistent with a Mannich-like addition between the pyrimidine nucleobase and the iminium intermediate of enzyme (Lys166) and open-chain pentose 5-phosphate. β-Elimination of the lysine and stereoselective ring closure give the product. We demonstrate phosphorylation-glycosylation cascade reactions for efficient, one-pot synthesis of C-nucleoside phosphates (yield: 33 - 94%) from unprotected sugar and nucleobase. We show incorporation of the enzymatically synthesized C-nucleotide triphosphates into nucleic acids by RNA polymerase. Collectively, these findings implement biocatalytic methodology for C-nucleotide synthesis which can facilitate XNA engineering for synthetic biology applications.

Nanomedicine-Based Approaches for mRNA Delivery

Messenger RNA (mRNA) has immense potential for developing a wide range of therapies, including immunotherapy and protein replacement. As mRNA presents no risk of integration into the host genome and does not require nuclear entry for transfection, which allows protein production even in nondividing cells, mRNA-based approaches can be envisioned as safe and practical therapeutic strategies. Nevertheless, mRNA presents unfavorable characteristics, such as large size, immunogenicity, limited cellular uptake, and sensitivity to enzymatic degradation, which hinder its use as a therapeutic agent. While mRNA stability and immunogenicity have been ameliorated by direct modifications on the mRNA structure, further improvements in mRNA delivery are still needed for promoting its activity in biological settings. In this regard, nanomedicine has shown the ability for spatiotemporally controlling the function of a myriad of bioactive agents in vivo. Direct engineering of nanomedicine structures for loading, protecting, and releasing mRNA and navigating in biological environments can then be applied for promoting mRNA translation toward the development of effective treatments. Here, we review recent approaches aimed at enhancing mRNA function and its delivery through nanomedicines, with particular emphasis on their applications and eventual clinical translation.

Phosphorothioate Modification of mRNA Accelerates the Rate of Translation Initiation to Provide More Efficient Protein Synthesis

Messenger RNAs (mRNAs) with phosphorothioate modification (PS-mRNA) to the phosphate site of A, G, C, and U with all 16 possible combinations were prepared, and the translation reaction was evaluated using an E. coli cell-free translation system. Protein synthesis from PS-mRNA increased in 12 of 15 patterns when compared with that of unmodified mRNA. The protein yield increased 22-fold when the phosphorothioate modification at A/C sites was introduced into the region from the 5'-end to the initiation codon. Single-turnover analysis of PS-mRNA translation showed that phosphorothioate modification increases the number of translating ribosomes, thus suggesting that the rate of translation initiation (rate of ribosome complex formation) is positively affected by the modification. The method provides a new strategy for improving translation by using non-natural mRNA.

Mesenchymal stem cells injected into carotid artery to target focal brain injury home to perivascular space

Rationale: The groundbreaking discovery of mesenchymal stem cells (MSCs) with their multifaceted benefits led to their widespread application in experimental medicine, including neurology. Efficient delivery of MSCs to damaged regions of the central nervous system may be a critical factor in determining outcome. Integrin VLA-4 (α4β1) coded by ITGA4 and ITGB1 genes is an adhesion molecule expressed by leukocytes, which is responsible for initiation of their diapedesis through cell docking to the inflamed vessel wall expressing VCAM1 receptor. This function of VLA-4 has been recapitulated in neural stem cells and glial progenitors. Thus, it was prudent to investigate this tool as a vehicle driving extravasation of MSCs. Since MSCs naturally express ITGB1 subunit, we decided to supplement them with ITGA4 only. The purpose of our current study is to investigate the eventual fate of IA delivered ITGA4 engineered and naive MSCs.

Methods: mRNA-ITGA4 transfected and naive MSCs were injected to right internal carotid artery of rats with focal brain injury. Through next three days MSC presence in animals' brain was navigated by magnetic resonance imaging. Transplanted cell location relative to the brain blood vessels and host immunological reaction were analyzed post-mortem by immunohistochemistry. The chemotaxis of modified and naive MSCs was additionally examined in in vitro transwell migration assay.

Results: Both naïve and ITGA4-overexpressing cells remained inside the vascular lumen over the first two days after IA infusion. On the third day, 39% of mRNA-ITGA4 modified and 51% naïve MSCs homed to perivascular space in the injury region (p=NS). The gradual decrease of both naive and mRNA-ITGA4 transfected hBM-MSCs in the rat brain was observed. mRNA-ITGA4 transfected MSCs appeared to be more vulnerable to phagocytosis than naïve cells. Moreover, in vitro study revealed that homogenate from the injured brain repels migration of MSCs, corroborating the incomplete extravasation observed in vivo.

Conclusions: In summary, IA transplanted MSCs are capable of homing to the perivascular space, an integral part of neurovascular unit, which might contribute to the replacement of injured pericytes, a critical element facilitating restoration of CNS function. The mRNA-ITGA4 transfection improves cell docking to vessel but this net benefit vanishes over the next two days due to fast clearance from cerebral vessels of the majority of transplanted cells, regardless of their engineering status. The drawbacks of mRNA-ITGA4 transfection become apparent on day 3 post transplantation due to the lower survival and higher vulnerability to host immune attack.

Co-delivery of NS1 and BMP2 mRNAs to murine pluripotent stem cells leads to enhanced BMP-2 expression and osteogenic differentiation

Application of messenger RNA (mRNA) for bone regeneration is a promising alternative to DNA, recombinant proteins and peptides. However, exogenous in vitro transcribed mRNA (IVT mRNA) triggers innate immune response resulting in mRNA degradation and translation inhibition. Inspired by the ability of viral immune evasion proteins to inhibit host cell responses against viral RNA, we applied non-structural protein-1 (NS1) from Influenza A virus (A/Texas/36/1991) as an IVT mRNA enhancer. We evidenced a dose-dependent blocking of RNA sensors by NS1 expression. The co-delivery of NS1 mRNA with mRNA of reporter genes significantly increased the translation efficiency. Interestingly, unlike the use of nucleosides modification, NS1-mediated mRNA translation enhancement does not dependent to cell type. Dual delivery of NS1 mRNA and BMP-2 mRNA to murine pluripotent stem cells (C3H10T1/2), promoted osteogenic differentiation evidenced by enhanced expression of osteoblastic markers (e.g. alkaline phosphatase, type I collagen, osteopontin, and osteocalcin), and extracellular mineralization. Overall, these results support the adjuvant potentiality of NS1 for mRNA-based regenerative therapies. STATEMENT OF SIGNIFICANCE: mRNA therapy has the potential to improve the efficiency of nucleic acid based regenerative medicine. Up to now, the incorporation of expensive modified nucleotides is a common way to avoid IVT mRNA-induced detrimental immunogenicity. We here introduce co-delivery of Influenza virus immune evasion protein-NS1 coding mRNA as a strategy to suppress RNA sensors for maximizing IVT mRNA expression. An increased osteogenic commitment of pluripotent stem cells was observed after BMP2 mRNA and NS1 mRNA delivery. This study revealed how applying non-modified mRNA with NS1 could be a promising alternative as a therapeutic in bone regeneration.

Enzymatic covalent labeling of RNA with RNA transglycosylation at guanosine (RNA-TAG)

Technologies for the labeling, detection, and manipulation of biomolecules have drastically improved our understanding of cell biology. As the myriad of functional roles for RNA in the cell are increasingly recognized, such tools to enable further investigation of RNA are the subject of much interest. RNA-TAG is an enzymatic method for site-specific, covalent labeling of RNA. This methodology makes use of a bacterial tRNA modifying enzyme, tRNA guanine transglycosylase, to incorporate modified substrate analogs into a target RNA, resulting in highly efficient and site-specific RNA labeling. In this chapter, we introduce the underlying principles of the RNA labeling reaction, discuss various applications of RNA-TAG, and present protocols for labeling specific RNA transcripts using this system.

Folate-Targeted mRNA Delivery Using Chitosan-Functionalized Selenium Nanoparticles: Potential in Cancer Immunotherapy

Systemic messenger RNA (mRNA) delivery, although still in its infancy, holds immense potential for application in cancer vaccination and immunotherapy. Its advantages over DNA transfection make it attractive in applications where transient expression is desired. However, this has proved challenging due to mRNA's instability and susceptibility to degradation. Selenium is important for immune function and modulation, with selenium nanoparticles (SeNPs) finding a niche in biomedicine as drug delivery vehicles, owing to their biocompatibility, low toxicity, and biodegradability. In this investigation, we synthesized chitosan-coated SeNPs with a folic acid targeting moiety for Fluc mRNA delivery to cancer cells in vitro. Synthesized SeNPs were stable and well dispersed, and ranged from 59 to 102 nm in size. Nanoparticles bound and protected mRNA from RNase degradation, while exhibiting low cytotoxicity in the human embryonic kidney (HEK293), breast adenocarcinoma (MCF-7), and nasopharyngeal (KB) cells in culture. Moderate cytotoxicity evidenced in the colorectal carcinoma (Caco-2) and colon carcinoma (HT-29) cells was attributed to apoptosis induction by selenium, as confirmed by acridine orange/ethidium bromide staining. Selenium uptake studies corroborated the transfection results, where significant transgene expression was evident for the overexpressed folate receptor-positive KB cells when compared to the other cells with less or no folate receptors.

Effective mRNA pulmonary delivery by dry powder formulation of PEGylated synthetic KL4 peptide

Pulmonary delivery of messenger RNA (mRNA) has considerable potential as therapy or vaccine for a range of lung diseases. Inhaled dry powder formulation of mRNA is particularly attractive as it has superior stability and dry powder inhaler is relatively easy to use. A safe and effective mRNA delivery vector as well as a suitable particle engineering method are required to produce a dry powder formulation that is respirable and mediates robust transfection in the lung. Here, we introduce a novel RNA delivery vector, PEG₁₂KL4, in which the synthetic cationic KL4 peptide is attached to a monodisperse linear PEG of 12-mers. The PEG₁₂KL4 formed nano-sized complexes with mRNA at 10:1 ratio (w/w) and mediated effective transfection on human lung epithelial cells. PEG₁₂KL4/mRNA complexes were successfully formulated into dry powder by spray drying (SD) and spray freeze drying (SFD) techniques. Both SD and SFD powder exhibited satisfactory aerosol properties for inhalation. More importantly, the biological activity of the PEG₁₂KL4 /mRNA complexes were successfully preserved after drying. Using luciferase mRNA, the intratracheal administration of the liquid or powder aerosol of PEG₁₂KL4 /mRNA complexes at a dose of 5μg mRNA resulted in luciferase expression in the deep lung region of mice 24h post-transfection. The transfection efficiency was superior to naked mRNA or lipoplexes (Lipofectamine 2000), in which luciferase expression was weaker and restricted to the tracheal region only. There was no sign of inflammatory response or toxicity of the PEG₁₂KL4 /mRNA complexes after single intratracheal administration. Overall, PEG₁₂KL4 is an excellent mRNA transfection agent for pulmonary delivery. This is also the first study that successfully demonstrates the preparation of inhalable dry powder mRNA formulations with in vivo transfection efficiency, showing the great promise of PEG₁₂KL4 peptide as a mRNA delivery vector candidate for clinical applications.

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

Ribonuclease (RNase)-mediated degradation of messenger RNA (mRNA) poses a huge obstruction to in vivo mRNA delivery. Herein, we propose a novel strategy to protect mRNA by structuring mRNA to prevent RNase attack through steric hinderance. Bundling of mRNA strands through hybridization of RNA oligonucleotide linkers allowed the preparation of mRNA nano-assemblies (R-NAs) comprised of 7.7 mRNA strands on average, mostly below 100 nm in diameter. R-NA formation boosted RNase stability by around 100-fold compared to naïve mRNA and preserved translational activity, allowing protein production. A mechanistic analysis suggests that an endogenous mRNA unwinding mechanism triggered by 5'-cap-dependent translation may induce selective R-NA dissociation intracellularly, leading to smooth translation. R-NAs showed efficient mRNA transfection in mouse brain, demonstrating the feasibility for in vivo administration.

mRNA: A Novel Avenue to Antibody Therapy?

First attempts to use exogenous mRNA for protein expression in vivo were made more than 25 years ago. However, widespread appreciation of in vitro transcribed mRNA as a powerful technology for supplying therapeutic proteins to the body has evolved only during the past few years. Various approaches to turning mRNA into a potent therapeutic have been developed. All of them share utilization of specifically designed, rather than endogenous, sequences and thorough purification protocols. Apart from this, there are two fundamental philosophies, one promoting the use of chemically modified nucleotides, the other advocating restriction to unmodified building blocks. Meanwhile, both strategies have received broad support by successful mRNA-based protein treatments in animal models. For such in vivo use, specifically optimized mRNA had to be combined with potent formulations to enable efficient in vivo delivery. The present review analyzes the applicability of mRNA technology to antibody therapy in all main fields: antitoxins, infectious diseases, and oncology.

PEG-OligoRNA Hybridization of mRNA for Developing Sterically Stable Lipid Nanoparticles toward In Vivo Administration

Lipid nanoparticles (LNPs) exhibit high potential as carriers of messenger RNA (mRNA). However, the arduous preparation process of mRNA-loaded LNPs remains a huge obstacle for their widespread clinical application. Herein, we tackled this issue by mRNA PEGylation through hybridization with polyethylene glycol (PEG)-conjugated RNA oligonucleotides (PEG-OligoRNAs). Importantly, mRNA translational activity was preserved even after hybridization of 20 PEG-OligoRNAs per mRNA. The straightforward mixing of the PEGylated mRNA with lipofectamine LTX, a commercial lipid-based carrier, just by pipetting in aqueous solution, allowed the successful preparation of mRNA-loaded LNPs with a diameter below 100 nm, whereas the use of non-PEGylated mRNA provided large aggregates above 100- and 1000-nm. In vivo, LNPs prepared from PEG-OligoRNA-hybridized mRNA exhibited high structural stability in biological milieu, without forming detectable aggregates in mouse blood after intravenous injection. In contrast, LNPs from non-PEGylated mRNA formed several micrometer-sized aggregates in blood, leading to rapid clearance from blood circulation and deposition of the aggregates in lung capillaries. Our strategy of mRNA PEGylation was also versatile to prevent aggregation of another type of mRNA-loaded LNP, DOTAP/Chol liposomes. Together, our approach provides a simple and robust preparation method to LNPs for in vivo application.

Design concepts of polyplex micelles for in vivo therapeutic delivery of plasmid DNA and messenger RNA

Nonviral delivery of plasmid (p)DNA or messenger (m)RNA is a safe and promising therapeutic option to continuously supply therapeutic proteins into diseased tissues. In most cases of in vivo pDNA and mRNA delivery, these nucleic acids are loaded into carriers based on cationic polymers and/or lipids to prevent nuclease-mediated degradation before reaching target cells. The carriers should also evade host clearance mechanisms, including uptake by scavenger cells and filtration in the spleen. Installation of ligands onto the carriers can facilitate their rapid uptake into target cells. Meanwhile, carrier toxicity should be minimized not only for preventing undesirable adverse responses in patients, but also for preserving the function of transfected cells to exert therapeutic effects. Long-term progressive improvement of platform technologies has helped overcome most of these issues, though some still remain hindering the widespread clinical application of nonviral pDNA and mRNA delivery. This review discusses design concepts of nonviral carriers for in vivo delivery and the issues to be overcome, focusing especially on our own efforts using polyplex micelles. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 978-990, 2019.

Induced packaging of mRNA into polyplex micelles by regulated hybridization with a small number of cholesteryl RNA oligonucleotides directed enhanced in vivo transfection

There has been a progressive interest in the molecular design of polymers and lipids as synthetic carriers for targeting therapeutic mRNA in vivo with the ability to circumvent nuclease attack for treating intractable diseases. Herein, we developed a simple approach to attain one order of magnitude higher nuclease tolerability of mRNA through the formation of polyplex micelles (PMs) by combining ω-cholesteryl (ω-Chol)-poly (ethylene-glycol) (PEG)-polycation block copolymers with mRNA pre-hybridized with cholesterol (Chol)-tethered RNA oligonucleotides (Chol (+)-OligoRNA). Even one or a few short Chol (+)-OligoRNA anchors harboring along the 46-fold longer mRNA strand was sufficient to induce tight mRNA packaging in the PM core, as evidenced by Förster resonance energy transfer (FRET) measurement as well as by a longitudinal relaxation time (T₁) measurement using NMR. These results suggest that Chol (+)-OligoRNA on mRNA strand serves as a node to attract ω-Chol moiety of the block copolymers to tighten the mRNA packaging in the PM core. These mRNA loaded PMs showed high tolerability against nuclease attack, and exerted appreciable protein translational activity in cultured cells without any inflammatory responses, achieved by shortening of the length of hybridizing Chol (+)-OligoRNAs to 17 nucleotides. Finally, the Chol (+)-OligoRNA-stabilized PM revealed efficient mRNA introduction into the mouse lungs via intratracheal administration, demonstrating in vivo utility of this formulation.

Optimization of CRISPR/Cas9 Delivery to Human Hematopoietic Stem and Progenitor Cells for Therapeutic Genomic Rearrangements

Editing the β-globin locus in hematopoietic stem cells is an alternative therapeutic approach for gene therapy of β-thalassemia and sickle cell disease. Using the CRISPR/Cas9 system, we genetically modified human hematopoietic stem and progenitor cells (HSPCs) to mimic the large rearrangements in the β-globin locus associated with hereditary persistence of fetal hemoglobin (HPFH), a condition that mitigates the clinical phenotype of patients with β-hemoglobinopathies. We optimized and compared the efficiency of plasmid-, lentiviral vector (LV)-, RNA-, and ribonucleoprotein complex (RNP)-based methods to deliver the CRISPR/Cas9 system into HSPCs. Plasmid delivery of Cas9 and gRNA pairs targeting two HPFH-like regions led to high frequency of genomic rearrangements and HbF reactivation in erythroblasts derived from sorted, Cas9+ HSPCs but was associated with significant cell toxicity. RNA-mediated delivery of CRISPR/Cas9 was similarly toxic but much less efficient in editing the β-globin locus. Transduction of HSPCs by LVs expressing Cas9 and gRNA pairs was robust and minimally toxic but resulted in poor genome-editing efficiency. Ribonucleoprotein (RNP)-based delivery of CRISPR/Cas9 exhibited a good balance between cytotoxicity and efficiency of genomic rearrangements as compared to the other delivery systems and resulted in HbF upregulation in erythroblasts derived from unselected edited HSPCs.

mRNA as novel technology for passive immunotherapy

While active immunization elicits a lasting immune response by the body, passive immunotherapy transiently equips the body with exogenously generated immunological effectors in the form of either target-specific antibodies or lymphocytes functionalized with target-specific receptors. In either case, administration or expression of recombinant proteins plays a fundamental role. mRNA prepared by in vitro transcription (IVT) is increasingly appreciated as a drug substance for delivery of recombinant proteins. With its biological role as transient carrier of genetic information translated into protein in the cytoplasm, therapeutic application of mRNA combines several advantages. For example, compared to transfected DNA, mRNA harbors inherent safety features. It is not associated with the risk of inducing genomic changes and potential adverse effects are only temporary due to its transient nature. Compared to the administration of recombinant proteins produced in bioreactors, mRNA allows supplying proteins that are difficult to manufacture and offers extended pharmacokinetics for short-lived proteins. Based on great progress in understanding and manipulating mRNA properties, efficacy data in various models have now demonstrated that IVT mRNA constitutes a potent and flexible platform technology. Starting with an introduction into passive immunotherapy, this review summarizes the current status of IVT mRNA technology and its application to such immunological interventions.

Messenger RNA Delivery for Tissue Engineering and Regenerative Medicine Applications

The ability to control cellular processes and precisely direct cellular reprogramming has revolutionized regenerative medicine. Recent advances in in vitro transcribed (IVT) mRNA technology with chemical modifications have led to development of methods that control spatiotemporal gene expression. Additionally, there is a current thrust toward the development of safe, integration-free approaches to gene therapy for translational purposes. In this review, we describe strategies of synthetic IVT mRNA modifications and nonviral technologies for intracellular delivery. We provide insights into the current tissue engineering approaches that use a hydrogel scaffold with genetic material. Furthermore, we discuss the transformative potential of novel mRNA formulations that when embedded in hydrogels can trigger controlled genetic manipulation to regenerate tissues and organs in vitro and in vivo. The role of mRNA delivery in vascularization, cytoprotection, and Cas9-mediated xenotransplantation is additionally highlighted. Harmonizing mRNA delivery vehicle interactions with polymeric scaffolds can be used to present genetic cues that lead to precise command over cellular reprogramming, differentiation, and secretome activity of stem cells-an ultimate goal for tissue engineering.

Nucleotide Modification Alters MicroRNA-Dependent Silencing of MicroRNA Switches

mRNA therapeutics hold great promise for the treatment of human diseases. While incorporating naturally occurring modified nucleotides during synthesis has greatly increased their potency and safety, challenges in selective expression have hindered clinical applications. MicroRNA (miRNA)-regulated in vitro-transcribed mRNAs, called miRNA switches, have been used to control the expression of exogenous mRNA in a cell-selective manner. However, the effect of nucleotide modifications on miRNA-dependent silencing has not been examined. Here we show that the incorporation of pseudouridine, N1-methylpseudourdine, or pseudouridine and 5-methylcytidine, which increases translation, tends to decrease the regulation of miRNA switches. Moreover, pseudouridine and 5-methylcytidine modification enables one miRNA target site at the 3′ UTR to be as effective as four target sites. We also demonstrate that the effects of pseudouridine, pseudouridine and 5-methylcytidine, and N1-methylpseudourdine modification are miRNA switch specific and do not correlate with the proportion of modified nucleotides in the miRNA target site. Furthermore, modified miRNA switches containing seed-complementary target sites are poorly regulated by miRNA. We also show that placing the miRNA target site in the 5′ UTR of the miRNA switch abolishes the effect of nucleotide modification on miRNA-dependent silencing. This work provides insights into the influence of nucleotide modifications on miRNA-dependent silencing and informs the design of optimal miRNA switches.

Biomedical applications of mRNA nanomedicine

As an attractive alternative to plasmid DNA, messenger RNA (mRNA) has recently emerged as a promising class of nucleic acid therapeutics for biomedical applications. Advances in addressing the inherent shortcomings of mRNA and in the development of nanoparticle-based delivery systems have prompted the development and clinical translation of mRNA-based medicines. In this review, we discuss the chemical modification strategies of mRNA to improve its stability, minimize immune responses, and enhance translational efficacy. We also highlight recent progress in nanoparticle-based mRNA delivery. Considerable attention is given to the increasingly widespread applications of mRNA nanomedicine in the biomedical fields of vaccination, protein-replacement therapy, gene editing, and cellular reprogramming and engineering.

In Vitro Transcribed mRNA Vaccines with Programmable Stimulation of Innate Immunity

In vitro transcribed (IVT) mRNA is an appealing platform for next generation vaccines, as it can be manufactured rapidly at large scale to meet emerging pathogens. However, its performance as a robust vaccine is strengthened by supplemental immune stimulation, which is typically provided by adjuvant formulations that facilitate delivery and stimulate immune responses. Here, we present a strategy for increasing translation of a model IVT mRNA vaccine while simultaneously modulating its immune-stimulatory properties in a programmable fashion, without relying on delivery vehicle formulations. Substitution of uridine with the modified base N1-methylpseudouridine reduces the intrinsic immune stimulation of the IVT mRNA and enhances antigen translation. Tethering adjuvants to naked IVT mRNA through antisense nucleotides boosts the immunostimulatory properties of adjuvants in vitro, without impairing transgene production or adjuvant activity. In vivo, intramuscular injection of tethered IVT mRNA-TLR7 agonists leads to enhanced local immune responses, and to antigen-specific cell-mediated and humoral responses. We believe this system represents a potential platform compatible with any adjuvant of interest to enable specific programmable stimulation of immune responses.