Head to Tail Analysis of mRNA by RapiZyme™ MC1 and Cusativin

Significance of the topic

Comprehensive characterization of messenger RNA (mRNA) therapeutics is essential for ensuring product quality, safety and consistent biological performance. Two critical quality attributes (CQAs) — the 5 cap structure and poly(A) tail integrity — strongly influence mRNA stability, translational efficiency and potency. Conventional approaches frequently require multiple, orthogonal workflows and extensive sample handling to evaluate these attributes along with sequence identity. The work summarized here demonstrates a consolidated enzymatic digestion strategy that enables simultaneous assessment of 5 capping, poly(A) tail length/heterogeneity and sequence coverage in a single LCMS workflow, reducing analytical complexity and accelerating CQA characterization.

Objectives and overview of the study

The study aimed to validate a unified digestion and LCMS approach for head-to-tail mRNA characterization using two complementary nucleases, RapiZyme MC1 and RapiZyme Cusativin. Specific goals were to:

• Identify and quantify 5 cap species and capping-related impurities;
• Determine poly(A) tail length distribution and detect sequence heterogeneity within tails;
• Obtain high sequence coverage for identity confirmation of the mRNA coding region;
• Demonstrate an integrated analytic pipeline coupling digestion, high-resolution LCMS and informatics tools to report CQAs in a streamlined workflow.

The test material was Firefly Luciferase (FLuc) mRNA in both unmodified and N1-methylpseudouridine (m1Ψ)-modified forms, produced by in vitro transcription (IVT).

Methodology and experimental design

The experimental strategy combined heat-denaturation of mRNA, enzymatic digestion with RapiZyme MC1 or Cusativin, IP-RP UPLC separation and high-resolution MS and DIA (MSE) acquisition, followed by integrated data processing in waters_connect applications. Key steps and conditions included:

• Sample preparation: 20 µg mRNA denatured at 90 °C for 2 min and cooled on ice;
• Digestions: ~300 U (15 U/µg) enzyme for unmodified RNA and ~600 U (30 U/µg) for m1Ψ-modified RNA in 60 µL of 100 mM ammonium acetate (pH 8.0 for MC1, pH 9.0 for Cusativin), incubated 30 °C for 60 min; enzymes heat-inactivated (MC1 70 °C, Cusativin 75 °C, 15 min);
• Chromatography: ACQUITY Premier Oligonucleotide BEH C18 (2.1×150 mm, 1.7 µm) at 70 °C, flow 0.4 mL/min, ion-pair mobile phases based on DIPEA/HFIP with acetonitrile in B; 10 µL injections;
• Mass spectrometry: Xevo MRT, ESI-, MSE acquisition m/z 50 4000, low CE 6 V, high CE ramp 25 45 V; data-dependent deconvolution and MS/MS confirmation;
• Data analysis: waters_connect suite including INTACT Mass App for cap and poly(A) analysis, CONFIRM Sequence for MS/MS verification, Synthetic Library for in silico digestion prediction, and MAP Sequence to integrate MC1 and Cusativin digests and compute sequence coverage.

Used instrumentation

• UPLC: ACQUITY Premier UPLC System (Binary Solvent Manager, Sample Manager FTN, ACQUITY TUV detector).
• Column: ACQUITY Premier Oligonucleotide BEH C18, 130 C, 1.7 m, 2.1 mm 150 mm.
• MS: Xevo MRT Mass Spectrometer, electrospray ionization in negative mode, MSE (data independent acquisition).
• Consumables and solvents: HFIP/DIPEA ion-pair reagents and nuclease-free water; QuanRecovery vials with MaxPeak HPS surfaces.
• Informatics: waters_connect platform (INTACT Mass, CONFIRM Sequence, Synthetic Library, MAP Sequence).

Main results and discussion

5 capping analysis:

• RapiZyme MC1 digestion produced definable oligonucleotide fragments that allowed discrimination of fully capped Cap1 species, uncapped species and capping-related impurities (e.g., pNm species) by intact mass and MS/MS fragment confirmation.
• Measured cap distribution showed high capping efficiency: unmodified FLuc contained ~98.4% Cap1, 1.35% pNm impurity and 0.23% uncapped species; m1Ψ-modified FLuc exhibited ~98.8% Cap1 and 1.17% uncapped, indicating robust capping in both constructs.

Sequence identity and coverage:

• In silico digestion predictions combined with experimental MC1 and Cusativin digests enabled integration of complementary cleavage products.
• Combined MC1/Cusativin analysis achieved 93% sequence coverage (excluding cap and poly(A)) for unmodified FLuc and 77.8% for m1Ψ-modified FLuc under the reported conditions; individual enzyme coverages were lower (MC1 ~82.9%, Cusativin ~67.5%), demonstrating synergistic benefit of dual digestion.
• Unassigned chromatographic peaks remain in both digests suggesting that additional manual interrogation or method optimization could further increase coverage.

Poly(A) tail length and heterogeneity:

• The poly(A) tail eluted as a distinct chromatographic peak and deconvolution revealed a distribution centered around a 111-mer (approx. 36.5 kDa), with detected lengths spanning ~104 114 nt.
• Spectral fine structure exhibited triplet peak patterns separated by ~24 Da increments consistent with one or two rA > rC substitutions per tail length. These variants likely reflect incorporation of CTP by E. coli poly(A) polymerase during enzymatic tailing and were resolvable by LCMS and INTACT Mass processing.

Overall, the dual-enzyme digestion workflow plus high-resolution MSE acquisition and integrated informatics provided a consolidated readout of multiple head-to-tail CQAs from a single sample preparation.

Benefits and practical applications

• Single, streamlined workflow that concurrently reports 5 capping status, poly(A) tail length/composition and sequence identity, reducing assay time and sample handling compared to separate orthogonal methods.
• High-resolution MS and MSE fragmentation enable confident assignment of cap structures and sequence confirmation without extensive additional enzymatic manipulations.
• Complementary cleavage specificities of MC1 and Cusativin increase overall sequence coverage, which is valuable for identity testing and impurity mapping of long mRNA constructs.
• Detection of poly(A) sequence variants (rA > rC substitutions) supports characterization of tailing reagent fidelity and process-related heterogeneity, informing manufacturing control strategies.
• Integration with informatics tools automates identification, quantitation and reporting of CQAs appropriate for both development and regulated environments.

Future trends and potential uses

• Optimization of digestion conditions and deeper MS/MS acquisition strategies could further increase sequence coverage, especially for chemically modified nucleotides such as m1Ψ.
• Adapting this workflow to broader classes of RNA therapeutics (self-amplifying RNA, circular RNA, longer UTR constructs) and to clinical QC/lot-release testing may improve throughput and harmonize analytics across product formats.
• Advances in informatics (automated peak assignment, improved fragmentation models for modified nucleotides) and higher-resolution instruments will enhance sensitivity for low-abundance impurities and sequence variants.
• Combining orthogonal chemistries or targeted enrichment strategies prior to LCMS could help identify rare truncations or sequence-specific modifications affecting function.

Conclusion

The combined use of RapiZyme MC1 and Cusativin with IPRP UPLC-MSE and a dedicated informatics suite enables a consolidated head-to-tail analysis of mRNA that simultaneously reports 5 cap identity and abundance, poly(A) tail length and heterogeneity, and extensive sequence coverage. This integrated approach streamlines CQA assessment for mRNA therapeutics, reduces analytical complexity and provides actionable information relevant for process development, release testing and troubleshooting of IVT and post-transcriptional modifications.

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