Characterization and Impurity Profiling of Combined Amylin and GLP-1 Analogs with RapiZyme Trypsin

Importance of the Topic

Peptide therapeutics targeting metabolic receptors such as GLP-1 and amylin are emerging treatments for type 2 diabetes and obesity. Fatty acid modifications enhance their potency but complicate reversed-phase chromatographic impurity analysis due to increased hydrophobicity. Combined lipopeptide drugs that engage multiple receptors require robust analytical workflows to ensure purity, identify degradation products and support regulatory compliance.

Objectives and Study Overview

This application note demonstrates a bottom-up characterization and impurity profiling strategy for a combined amylin/GLP-1 analog formulation (cagrilintide + semaglutide) using Waters RapiZyme Trypsin and LC-MS. Key goals include:

• Achieve complete proteolysis (>99.5%) of both peptides.
• Improve chromatographic resolution of minor modified species.
• Localize and tentatively identify deamidation impurities.

Instrumentation and Methodology

Proteolytic digestion: Samples of cagrilintide and semaglutide were mixed in Tris-HCl (pH 7.5), treated with N-ethylmaleimide (NEM) to block free sulfhydryls, and incubated with RapiZyme Trypsin at 37 °C for 30 min. Partial reduction experiments using TCEP confirmed disulfide status.

LC-MS analysis: Digests were separated on an ACQUITY Premier Peptide CSH C18 column (2.1 × 150 mm, 1.7 µm) at 60 °C using a shallow gradient of 0.1% formic acid in water and acetonitrile. Detection was by PDA at 214 nm and ESI+ full-scan MS (50–2000 m/z) on a RDa detector. Waters_connect software managed data acquisition and processing.

Main Results and Discussion

• Complete digestion: Extracted ion chromatograms of observed tryptic peptides indicated >99.5% cleavage for both cagrilintide and semaglutide, overcoming co-elution challenges of intact lipopeptides.
• Improved resolution: Digested peptides bearing deamidation or other modifications were chromatographically separated, unlike the overlapping peaks in intact analysis.
• Impurity localization: An unknown +3 Da species detected in intact material was resolved into specific tryptic fragments. Deamidation sites were localized to C1 and C3 peptides of cagrilintide. Forced degradation at 50 °C confirmed the identity of singly deamidated C3 and provided insights into additional +2 Da modifications on C1.

Benefits and Practical Applications

• Rapid bottom-up peptide mapping of multi-agonist lipopeptides.
• High digestion efficiency enables sensitive impurity tracking.
• Enhanced separation and MS detection of minor degradants support quality control and stability studies.

Future Trends and Potential Applications

Proteolytic profiling with immobilized or rapid-action enzymes is likely to expand for complex peptide conjugates and antibody–drug conjugates. Integration with high-resolution MS/MS and automated sample preparation will drive deeper sequence coverage, real-time monitoring of forced-degradation pathways and bioinformatics-driven impurity identification.

Conclusion

RapiZyme Trypsin combined with UPLC-MS provides a robust bottom-up approach for characterizing combined amylin/GLP-1 analogs. The method achieves near-complete digestion, enhances chromatographic separation of modified peptides and enables localization of deamidation impurities. This workflow supports comprehensive impurity profiling and stability assessment of advanced peptide therapeutics.

References

1. Watanabe J.H., Kown J., Nan B., Reikes A. Trends in glucagon-like peptide 1 receptor agonist use, 2014 to 2022. Journal of the American Pharmacists Association. 2024;64:133–138.
2. Novo Nordisk. CagriSema® triple agonist targets GLP-1, amylin and calcitonin receptors. Press release. 2024.