Differentiate Minor Difference of Protein Structure in Biosimilar and Reference Products Using High-Resolution Orbitrap LC-MS/MS

Importance of the Topic

Accurate differentiation of protein structural variants between biosimilar and reference biologic products is critical for ensuring clinical safety, therapeutic efficacy, and regulatory compliance. Minor changes in post-translational modifications such as glycosylation and deamidation can affect protein stability, immunogenicity, and function. High-resolution mass spectrometry provides an advanced analytical approach to detect and quantify these subtle differences.

Study Objectives and Overview

This study aimed to develop and validate a robust LC-MS/MS workflow for comprehensive comparison of a reference therapeutic protein (TPA) and two biosimilar candidates (I-TANK and G-TANK). The objectives included:

• Achieving full peptide sequence coverage for each product.
• Identifying and localizing glycosylation sites and deamidation events.
• Quantifying glycoform distributions across samples.
• Demonstrating qualitative and quantitative differentiation of product variants.

Methodology and Used Instrumentation

A top-ten data-dependent acquisition method with high-energy collision dissociation (HCD) was employed on a bench-top Thermo Scientific Q Exactive Quadrupole-Orbitrap mass spectrometer. Key elements included:

• Sample analysis in triplicate for each product, yielding nine raw LC-MS/MS files.
• High-resolution full MS and MS/MS spectra acquisition.
• Data processing using a newly developed software platform under evaluation.

Main Results and Discussion

Peptide Identification and Sequence Coverage:

• 100% protein sequence coverage achieved in all nine runs.
• 40–50% of MS/MS spectra matched peptides with high confidence.

Glycosylation Analysis:

• Three N-linked glycosylation sites (N103, N117, N448) were consistently observed with site occupancies >99%.
• Between 11 and 47 distinct glycoforms identified per site across samples.
• Quantitative differences in glycoform abundances were detected among TPA, I-TANK, and G-TANK, indicating biosimilar versus reference variation.

Deamidation Mapping:

• Two deamidation sites (N-140, N-142) on peptide 136–145 were localized and characterized by accurate mass shifts in HCD spectra.

Benefits and Practical Applications

This high-resolution LC-MS/MS workflow offers:

• Comprehensive structural characterization for biosimilar development and quality control.
• Sensitive detection of minor post-translational modifications impacting product performance.
• Support for regulatory submission dossiers by demonstrating product comparability.

Future Trends and Opportunities

Advances in software-driven data analysis, improved quantitation strategies, and automation will further enhance this workflow. Integration with ion mobility separation, targeted MS approaches, and application to other biologic modalities (e.g., antibody–drug conjugates) represents promising directions.

Conclusion

The presented Orbitrap-based LC-MS/MS method enables detailed, high-confidence differentiation of minor structural differences between biosimilar and reference protein products. It provides a valuable platform for both fundamental research and regulated biopharmaceutical quality assessment.

Reference

Hao Z, Horn DM, Wu S-L, Zhang F, Bennett P. Differentiate Minor Difference of Protein Structure in Biosimilar and Reference Products Using High-Resolution Orbitrap LC-MS/MS. Thermo Fisher Scientific; Barnett Institute.