Charge Heterogeneity Analysis of Rituximab Innovator and Biosimilar mAbs

Significance of the Topic

Monoclonal antibodies such as rituximab exhibit charge heterogeneity due to post-translational modifications, which can impact therapeutic efficacy, stability, and safety. Detailed charge variant profiling is critical in biopharmaceutical development and quality control, particularly when establishing biosimilarity.

Study Objectives and Overview

This application note describes a high-resolution cation exchange chromatography method to compare charge variant profiles of innovator and biosimilar rituximab. Carboxypeptidase B digestion is applied to confirm the identity of major basic variants.

Methodology

A salt-gradient cation exchange method was optimized using Agilent Buffer Advisor. Innovator and biosimilar rituximab (1 mg/mL) were analyzed on an Agilent 1260 Infinity Bio-inert Quaternary LC with a Bio MAb NP5 PEEK column (4.6 × 250 mm, 5 μm). Mobile phases consisted of water, NaCl (850 mM), NaH2PO4 (41 mM) and Na2HPO4 (55 mM) with a defined gradient over 21 minutes. Detection was performed at 280 nm with a 5 Hz acquisition rate. Carboxypeptidase B digestion (0.25 units, 37 °C, pH 7.5) was used to cleave C-terminal lysine residues before analysis.

Used Instrumentation

• Agilent 1260 Infinity Bio-inert Quaternary LC pump
• Agilent 1260 Infinity bio-inert autosampler
• Agilent 1200 Infinity thermostat and column compartment
• Agilent 1260 Infinity diode array detector with 10 mm flow cell
• Agilent OpenLAB ChemStation CDS and Buffer Advisor software

Main Results and Discussion

The chromatographic method achieved separation of acidic, main, and basic isoforms within 20 minutes. Innovator rituximab displayed 93.21% main form and 3.22% basic variants, while biosimilar showed only 29.78% main form and 69.46% basic variants. Retention time and area RSD values for the main peak were below 0.1% and 1.5%, respectively. Carboxypeptidase B treatment eliminated basic peaks, confirming their assignment as C-terminal lysine variants, and demonstrated comparable main-form profiles between innovator and digested biosimilar.

Benefits and Practical Applications

• Provides a robust, reproducible QC method for monitoring antibody charge variants
• Enables direct comparison of innovator and biosimilar products
• Supports regulatory compliance in biosimilar development

Future Trends and Applications

Emerging directions include coupling ion exchange chromatography with mass spectrometry for molecular identification, use of advanced weak cation exchange resins for higher resolution, automated method development via machine learning, and integration of two-dimensional LC workflows for deeper antibody characterization.

Conclusion

The described salt-gradient cation exchange method on a bio-inert LC platform offers high resolution, precision, and throughput for charge heterogeneity analysis of mAbs. Carboxypeptidase B digestion confirms lysine variant identity, making this approach valuable for QC and biosimilarity assessments.

Reference

1. Yan H, et al. J Sep Sci 2011, 34, 548–555
2. Agilent publication number 5991-0895EN
3. Agilent publication number 5990-6844EN
4. Agilent publication number 5991-0565EN