High resolution biosensor to test the capping level and integrity of mRNAs

High-Throughput Spectroscopic Analysis of mRNA Capping Level

Eukaryotic mRNAs are characterized by terminal 5' cap structures and 3' polyadenylation sites, which are essential for posttranscriptional processing, translation initiation, and stability. Here, we describe a novel biosensor method designed to detect the presence of both cap structures and polyadenylation sites on mRNA molecules. This novel biosensor is sensitive to mRNA degradation and can quantitatively determine capping levels of mRNA molecules within a mixture of capped and uncapped mRNA molecules. The biosensor displays a constant dynamic range between 254 nt and 6507 nt with reproducible sensitivity to increases in capping level of at least 20% and a limit of detection of 2.4 pmol of mRNA. Overall, the biosensor can provide key information about mRNA quality before mammalian cell transfection.

A systems-level mass spectrometry-based technique for accurate and sensitive quantification of the RNA cap epitranscriptome

Chemical modifications of transcripts with a 5' cap occur in all organisms and function in many aspects of RNA metabolism. To facilitate analysis of RNA caps, we developed a systems-level mass spectrometry-based technique, CapQuant, for accurate and sensitive quantification of the cap epitranscriptome. The protocol includes the addition of stable isotope-labeled cap nucleotides (CNs) to RNA, enzymatic hydrolysis of endogenous RNA to release CNs, and off-line enrichment of CNs by ion-pairing high-pressure liquid chromatography, followed by a 17 min chromatography-coupled tandem quadrupole mass spectrometry run for the identification and quantification of individual CNs. The total time required for the protocol can be up to 7 d. In this approach, 26 CNs can be quantified in eukaryotic poly(A)-tailed RNA, bacterial total RNA and viral RNA. This protocol can be modified to analyze other types of RNA and RNA from in vitro sources. CapQuant stands out from other methods in terms of superior specificity, sensitivity and accuracy, and it is not limited to individual caps nor does it require radiolabeling. Thanks to its unique capability of accurately and sensitively quantifying RNA caps on a systems level, CapQuant can reveal both the RNA cap landscape and the transcription start site distribution of capped RNA in a broad range of settings.

Challenges and emerging trends in liquid chromatography-based analyses of mRNA pharmaceuticals

Lipid encapsulated messenger RNA (LNP mRNA) has garnered a significant amount of interest from the pharmaceutical industry and general public alike. This attention has been catalyzed by the clinical success of LNP mRNA for SARS-CoV-2 vaccination as well as future promises that might be fulfilled by the biotechnology pipeline, such as the in vivo delivery of a CRISPR/Cas9 complex that can edit patient cells to reduce levels of low-density lipoprotein. LNP mRNAs are comprised of various chemically diverse molecules brought together in a sophisticated intermolecular complex. This can make it challenging to achieve thorough analytical characterization. Nevertheless, liquid chromatography is becoming an increasingly relied upon technique for LNP mRNA analyses. Although there have been significant advances in all types of LNP mRNA analyses, this review focuses on recent developments and the possibilities of applying anion exchange (AEX) and ion pairing reversed phase (IP-RP) liquid chromatography for intact mRNAs as well as techniques for oligo mapping analysis, 5' endcap testing and lipid compositional assays.

Low Resource Integrated Platform for Production and Analysis of Capped mRNA

The existing platform for large-scale mRNA production is fast, but consumable costs, process technicality, and complexity represent key bottlenecks limiting global mRNA biologics manufacturing. Another challenge is the lack of a consolidated platform for mRNA product characterization and assays that meet regulatory requirements. Bridging these innovation gaps to simplify processes and reduce cost would improve mRNA biologics manufacturability, especially in low-resource settings. This study develops a "cotranscriptional" capping strategy that utilizes T7 RNA polymerase, and the Vaccinia Capping System to synthesize and cap mRNA. We created an "integrated reaction buffer" that supports both capping enzymes for catalytic and in vitro transcription processes, enabling one-pot, two-step capped mRNA synthesis. Additionally, we report a novel, one-step analytic platform for rapid, quantitative, capped mRNA analysis. The assay involves target mRNA segment protection with cheap DNA primers and RNase digest of non-hybridized or non-target sequences before analysis by single nucleotide-resolving urea-polyacrylamide gel electrophoresis (PAGE). The integrated approach simplifies production processes and saves costs. Moreover, this assay has potential applications for mRNA analyses and post-transcriptional modification detection in biological samples. Finally, we propose a strategy that may enable unparalleled sequence coverage in RNase mass mapping by adapting the developed assay and replacing urea-PAGE with mass spectrometry.

A cap 0-dependent mRNA capture method to analyze the yeast transcriptome

Analysis of the protein coding transcriptome by the RNA sequencing requires either enrichment of the desired fraction of coding transcripts or depletion of the abundant non-coding fraction consisting mainly of rRNA. We propose an alternative mRNA enrichment strategy based on the RNA-binding properties of the human IFIT1, an antiviral protein recognizing cap 0 RNA. Here, we compare for Saccharomyces cerevisiae an IFIT1-based mRNA pull-down with yeast targeted rRNA depletion by the RiboMinus method. IFIT1-based RNA capture depletes rRNA more effectively, producing high quality RNA-seq data with an excellent coverage of the protein coding transcriptome, while depleting cap-less transcripts such as mitochondrial or some non-coding RNAs. We propose IFIT1 as a cost effective and versatile tool to prepare mRNA libraries for a variety of organisms with cap 0 mRNA ends, including diverse plants, fungi and eukaryotic microbes.

Ribozyme Assays to Quantify the Capping Efficiency of In Vitro-Transcribed mRNA

The presence of the cap structure on the 5′-end of in vitro-transcribed (IVT) mRNA determines its translation and stability, underpinning its use in therapeutics. Both enzymatic and co-transcriptional capping may lead to incomplete positioning of the cap on newly synthesized RNA molecules. IVT mRNAs are rapidly emerging as novel biologics, including recent vaccines against COVID-19 and vaccine candidates against other infectious diseases, as well as for cancer immunotherapies and protein replacement therapies. Quality control methods necessary for the preclinical and clinical stages of development of these therapeutics are under ongoing development. Here, we described a method to assess the presence of the cap structure of IVT mRNAs. We designed a set of ribozyme assays to specifically cleave IVT mRNAs at a unique position and release 5′-end capped or uncapped cleavage products up to 30 nt long. We purified these products using silica-based columns and visualized/quantified them using denaturing polyacrylamide gel electrophoresis (PAGE) or liquid chromatography and mass spectrometry (LC–MS). Using this technology, we determined the capping efficiencies of IVT mRNAs with different features, which include: Different cap structures, diverse 5′ untranslated regions, different nucleoside modifications, and diverse lengths. Taken together, the ribozyme cleavage assays we developed are fast and reliable for the analysis of capping efficiency for research and development purposes, as well as a general quality control for mRNA-based therapeutics.