Relating Protein-Protein Interactions and Aggregation Rates From Low to High Concentrations

Area of Science:

• Biophysical Chemistry
• Protein Science
• Pharmaceutical Development

Background:

• Non-native protein aggregation rates are sensitive to protein concentration, conformational stability, and protein-protein interactions.
• Understanding these interactions is crucial for predicting and controlling protein aggregation, particularly for therapeutic monoclonal antibodies (MAbs).

Purpose of the Study:

• To systematically quantify protein-protein interactions and aggregation rates for a MAb across a wide concentration range.
• To evaluate different theoretical hypotheses linking protein-protein interactions to aggregation rates.
• To identify predictive models for protein aggregation behavior.

Main Methods:

• Quantified aggregation rates using initial-rate analysis and size-exclusion chromatography.
• Measured protein-protein interactions via static and dynamic laser light scattering.
• Tested hypotheses based on thermodynamic activity, fluctuation theory, and surface-contact probabilities.

Main Results:

• Aggregation rates and protein-protein interactions were measured for a MAb at pH 5.1 and 6.5, with and without sucrose or NaCl.
• Hypotheses based on thermodynamic activity and fluctuation theory were inconsistent with experimental data.
• A model based on surface-contact probabilities showed a semiquantitative correlation with aggregation rates over two orders of magnitude of protein concentration.

Conclusions:

• Surface-contact probabilities, approximated by the Kirkwood-Buff integral, offer a promising approach for predicting MAb aggregation rates.
• This finding aids in understanding and controlling protein aggregation in biopharmaceutical development.
• Further refinement of the model may improve quantitative predictions.