Revisit PEG-Induced Precipitation Assay for Protein Solubility Assessment of Monoclonal Antibody Formulations

PurposeProtein solubility is an important attribute of pharmaceutical monoclonal antibody (MAb) formulations, particularly at high MAb concentrations. PEG-induced protein precipitation has been routinely used to assess protein solubility. To provide insights for better understanding and implementation of PEG-induced protein precipitation assay, this work compares different solubility measures and examines their relevance to loss of protein solubility in concentrated formulations.MethodsSolubility of a MAb in 15 formulations was evaluated using PEG-induced precipitation assay. Three apparent protein solubility measures, the middle-point and onset PEG concentrations (cmid and conset) as well as the binding free energy (μB), were obtained from the PEG-induced protein precipitation assay and compared to the DLS protein interaction parameter (kD). Visual inspection of loss of protein solubility in concentrated formulations during storage was used to further examine the discrepancy of protein solubility ranking by these measures.ResultsPEG-induced precipitation assay predicted overall protein solubility ranking similar to that by DLS kD. However, for three formulations with ionic excipients NaCl, Arg·Cl, and Arg·Glu·Cl, PEG-induced precipitation assay yielded more accurate predictions compared to DLS kD measurements. Furthermore, μB showed superior ability in distinguishing protein solubility for these formulations.ConclusionsThis study demonstrated good correlations between the protein solubility measures obtained from PEG-induced precipitation experiments and DLS kD measurement. It also provides one example in which protein solubility ranking by binding free energy is more accurate than the other measures. The results support the theoretical proposition that μB has a potential to serve as standard protein solubility measure.