Characterization of self-associating antibody solutions at high concentrations with CG-MALS

Importance of the Topic

Therapeutic monoclonal antibodies (mAbs) are increasingly formulated at high concentrations to meet dosage and delivery requirements. However, elevated protein concentrations often lead to unwanted viscosity and colloidal instability driven by weak self-interactions among antibody molecules. Understanding and quantifying these interactions is crucial for efficient formulation development, manufacturability, and patient compliance.

Goals and Overview of the Study

This study aimed to characterize the self-association behavior of three antibody formulations (mAb A, B, and C) in their native buffers. By applying automated composition-gradient multi-angle light scattering (CG-MALS), the authors sought to determine:

• Second virial coefficients (A2) reflecting repulsive interactions
• Equilibrium dissociation constants for dimerization and higher-order assembly
• Correlation between measured interaction parameters and solution viscosity

Methodology and Instrumentation

Automated CG-MALS measurements were performed using the following workflow:

• Preparation of antibody stock solutions in native formulation buffers
• Automated generation of 8–9 concentration points up to ~40 mg/mL via the Calypso concentration-gradient system
• Detection of scattered light by a DAWN MALS detector and refractive index by an Optilab dRI (high-concentration model)
• Supplementary high-concentration points measured in a microCuvette for mAbs B and C
• Data analysis and fitting to interaction models using CALYPSO software

Used Instrumentation

• Wyatt Calypso concentration-gradient autosampler
• Wyatt DAWN multi-angle light scattering detector
• Wyatt Optilab refractive index detector (HC model)
• MicroCuvette accessory for manual high-viscosity measurements

Main Results and Discussion

Key findings from the CG-MALS analysis include:

• mAb A exhibited purely repulsive behavior with A2 = 7.13×10–5 mol·mL/g², consistent with excluded-volume effects and a hydrodynamic radius ~5.5 nm
• mAb B and mAb C showed significant self-association: monomer-monomer dissociation constants of 280 µM (B) and 400 µM (C)
• Further isodesmic self-association of dimers yielded ISA Kd values of 180 µM (B) and 130 µM (C), indicating growth of higher-order oligomers
• Mass distributions revealed that oligomers above 10-mers remain below 1% molar fraction
• Viscosity measurements correlated with attractive interaction strength: lowest for mAb A (~3 cP at 100 mg/mL) and highest for mAb C (~13 cP at 150 mg/mL)
• Alternative modeling for mAb B (isodesmic self-association of monomers) provided a reasonable but slightly inferior fit compared to the dimer+ISA scheme

Benefits and Practical Applications

This characterization approach offers formulators:

• Rapid, label-free assessment of protein-protein interactions at formulation-relevant concentrations
• Quantitative parameters (A2, Kd values) to rank candidate antibodies by colloidal stability
• Early identification of viscosity liabilities to guide buffer optimization, excipient selection, or protein engineering

Future Trends and Applications

Potential directions building on this work include:

• High-throughput integration of CG-MALS in formulation screening pipelines
• Application to non-antibody biologics and complex mixtures
• Coupling interaction data with rheological models for predictive viscosity forecasting
• Use of advanced data analytics and machine learning to correlate sequence/structure features with self-association propensity

Conclusion

Automated CG-MALS using the Calypso system provides a powerful, noninvasive tool to dissect attractive and repulsive forces in high-concentration antibody solutions. The measured second virial coefficients and dissociation constants accurately predicted formulation viscosity trends for three mAbs. This methodology supports more informed decision-making in biologics development, reducing risks associated with high viscosity and aggregation.

Reference

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