Rapid Analysis of mRNA 5’-Capping with High-Resolution LC-MS

Importance of the Topic

Messenger RNA (mRNA) therapeutics rely on efficient translation into protein, which is critically governed by the presence and structure of the 5’ cap. Accurate and rapid measurement of capping efficiency is essential for quality control in industrial production, vaccine development, and RNA research. Traditional assays can be time-consuming and lack the resolution to distinguish intermediate cap structures, motivating the development of high-throughput chromatographic and mass-spectrometric workflows.

Objectives and Study Overview

This study presents a streamlined liquid chromatography–mass spectrometry (LC–MS) method for the rapid analysis of mRNA 5’ capping, aiming to:

• Reduce total analysis time to under 75 minutes.
• Separate uncapped, partially capped, and fully capped oligonucleotides.
• Quantify capping efficiency with high linearity and precision.
• Demonstrate applicability to both anti-reverse cap analog (ARCA) and Vaccinia enzyme capping processes.

Methodology

Sample preparation leverages thermostable RNase-H guided by 2’-O-methyl RNA/DNA chimeric probes to cleave full-length mRNA (~3800 nt) into 40–50 nt fragments containing the 5’ cap. Key steps include:

• Co-transcriptional ARCA capping or post-transcriptional enzymatic capping with Vaccinia capping enzyme.
• Annealing of chimeric probes and digestion at 50 °C via thermostable RNase-H (30 min), eliminating off-target products observed at 37 °C.
• C18-based cleanup (10 min).
• Reverse-phase ion-pairing LC separation (25 min) using HFIP and dibutylamine mobile phase.
• High-resolution MS detection and deconvolution in BioConfirm software (10 min).

Used Instrumentation

• Agilent 2100 Bioanalyzer for sizing and qualitative assessment.
• Agilent 6545XT AdvanceBio LC/Q-TOF mass spectrometer.
• AdvanceBio Oligonucleotide column (2.1 × 50 mm, 2.7 µm).

Main Results and Discussion

The method achieves clear baseline separation of uncapped, diphosphate/diphosphate intermediates, and fully capped oligonucleotides. Key findings include:

• Deconvoluted mass accuracy <10 ppm for 5’ diphosphate (16,131 Da) and triphosphate (16,211 Da) fragments.
• Linear response (R2 = 0.9999) across 5–80% capping ratios, with LLOQ ~8%.
• Inter-day capping ratio RSD ≤11% and retention time RSD ≤1.4%.
• Optimization of Vaccinia enzyme reaction increased Cap 0 yield from 2.6% to 32.9% by adjusting reactant:mRNA ratios.

Benefits and Practical Applications

Compared to conventional assays, the proposed workflow offers:

• Rapid turnaround (<75 min) suitable for in-process monitoring.
• High specificity for cap structures and sequence variants (e.g., transcriptional slippage +G forms).
• Quantitative robustness, supporting quality assurance in mRNA manufacturing.
• Flexibility to evaluate different capping chemistries and enzyme optimizations.

Future Trends and Opportunities

Advances may include integration of automated sample handling, extension to longer or modified RNA species, and coupling with UV or fluorescence detectors for orthogonal validation. Emerging ion-mobility separation and higher-resolution instruments could further resolve complex cap variants and epitranscriptomic modifications.

Conclusion

A high-resolution LC–MS method using thermostable RNase-H and IP-RP separation enables fast, accurate quantification of mRNA 5’ capping. With demonstrated linearity, reproducibility, and adaptability to ARCA and enzymatic capping, this platform supports rapid process development and quality control in RNA-based therapeutics.

Reference

1. Hassett KJ et al., Mol. Ther. Nucleic Acids, 2019, 15, 1–11.
2. Beverly M et al., Anal. Bioanal. Chem., 2016, 408, 5021–5030.
3. Fuchs AL et al., RNA, 2016, 22, 1454–1466.