Correlating High Concentration Behavior of Commercial or Clinical-Stage Monoclonal and Bispecific Antibodies with Miniaturized Polyethylene Glycol Precipitation Assay

Subcutaneous delivery of protein therapeutics often necessitates strict limitations on low injection volumes and high protein concentrations. As a result, achieving high protein solubility is a critical quality attribute for subcutaneous protein drug products. Direct characterization of protein solubility during the early stages of drug development, however, is often impractical due to limited sample availability. In this study, we investigated the utility of a miniaturized, high-throughput PEG precipitation (mini-PEG) screening assay for ranking the solubility of biologic drugs, including commercially approved and advanced clinical-stage monoclonal antibodies (mAbs) and bispecific antibodies. The apparent solubility determined using the mini-PEG precipitation assay was largely consistent with solubility in formulation without PEG and, to a lesser extent, with other physicochemical properties governed by protein-protein interactions. Further analysis with model proteins, such as NISTmAb, revealed a strong dependence of apparent solubility on buffer type, in addition to pH, likely due to the impact of buffer agents on ionic strength and potential preferential interactions between buffer species and protein molecules. In conclusion, the miniaturized, high-throughput PEG precipitation assay enables effective solubility rankings of biologic candidates and formulations during developability assessments, using only microgram quantities of samples.